Disposable, microwaveable containers having suitable food contact compatible olfactory properties and process for their manufacture

ABSTRACT

Low-odor microwaveable polypropylene/mica food contact articles are disclosed. The articles are prepared by low temperature processing and typically include odor-suppressing basic organic or inorganic compounds. Preferably, the articles are substantially free from C8 and C9 organic ketones associated with undesirable odors. Further improvements to the articles include crack-resistant embodiments with synergistic amounts of polyethylene and titanium dioxide.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation patent application ofdivisional patent application U.S. Ser. No. 09/767,082, filed Jan. 23,2001, now U.S Pat. No. 6,420,689, which was based upon U.S. Ser. No.09/267,716, filed Mar. 12, 1999, now U.S. Pat. No. 6,211,500 which was anon-provisional application based on U.S. Provisional Application Ser.No. 60/078,923, filed Mar. 20, 1998, of the same title, the prioritiesof which are hereby claimed.

BACKGROUND OF THE INVENTION

Filled polypropylene articles have been observed to exhibit undesirableodors, particularly upon heating. In this respect, see U.S. Pat. No.5,023,286 to Abe et al., wherein phenolic antioxidants are suggested tocontrol the odor problem. Other polypropylene compositions may be foundin U.S. Pat. Nos. 4,734,450 to Kawai et al.; U.S. Pat. No. 5,045,369 toKobayashi et al.; U.S. Pat. No. 5,300,747 of Simon; U.S. Pat. No.5,439,628 of Huang and U.S. Pat. No. 4,933,526 of Fisher et al.

This invention relates to disposable, polypropylene/mica microwaveablecontainers having suitable food contact compatible olfactory propertiesincluding cups, trays, souffle dishes, lids, plates, bowls, and relatedarticles of manufacture useful for preparation, storage, delivery, andserving of food, wherein convenience and low cost are of paramountimportance. Nevertheless, suitable food contact compatible olfactoryproperties, appearance, and tactile characteristics of the plate,container, etc., are important for consumer preference. The suitabilityof these disposable articles of manufacture for microwave cooking, orheating of food, has an important place in today's marketplace. Both thecommercial and retail market components need an aesthetically pleasingmicrowaveable, disposable, rigid and strong container, plate, or cup,and related articles of manufacture which also have suitable foodcontact compatible olfactory properties.

These disposable microwaveable containers and plates exhibit a meltingpoint of no less than about 250° F., the containers or plates beingdimensionally stable and resistant to grease, sugar and water attemperatures up to at least 220° F. and exhibiting sufficient toughnessto be resistant to cutting by serrated polystyrene flatware and alsoexhibiting food contact compatible olfactory properties. The preferredcontainers and plates exhibit both suitable food contact compatibleolfactory properties and at least one micronodular surface on the foodcontact side of the container or plate.

SUMMARY OF THE INVENTION

Microwaveable, disposable, rigid and strong containers and plates havingsuitable food contact compatible olfactory properties have beenprepared. These disposable and microwaveable articles of manufactureexhibit (a) suitable food contact compatible olfactory properties; and(b) a melting point of not less than 250° F., suitably 250° F. to 330°F. In preferred embodiments these articles of manufacture exhibit amicronodular surface on the side coming in contact with food. Thesemicrowaveable, food contact compatible containers and plates aredimensionally stable and resistant to grease, sugar and water attemperatures of at least 220° F. and are of sufficient toughness to beresistant to cutting by serrated polystyrene flatware. The containersand plates of this invention answer a long felt need for products whichcan withstand the severe conditions of a microwave oven when commonfoods such as beans and pork, pancakes with syrup, pepperoni pizza, andbroccoli with cheese are microwaved during food cooking andreconstituting processes.

It has been found in accordance with the present invention thatpolypropylene/mica food contact articles such as bowls or plates exhibitsuitable olfactory characteristics when prepared by a low temperatureprocess and/or when prepared including a basic organic or inorganiccompound. There is provided in a first aspect of the present invention,a microwaveable, disposable food service article having food contactcompatible olfactory properties formed of a melt processedpolyolefin/mica composition wherein the composition includes from about40 to about 90% by weight of a polypropylene polymer and from about 10to about 50% by weight mica where the melt processed compositionexhibits low odor as characterized by a relative aroma intensity indexof less than about 1.6. Less than about 1.5 is more preferred and, as apractical matter, the lower limit of the relative aroma intensity indexfor the inventive composition is believed to be about 0.1.

Typically, the melt processed composition from which the microwaveablearticle is formed also includes a basic organic or inorganic compoundincluding the reaction product of an alkali metal or alkaline earthelement with carbonates, phosphates, carboxylic acids as well as alkalimetal and alkaline earth element oxides, hydroxides, or silicates andbasic metal oxides including mixtures of silicone dioxide with one ormore of the following oxides: magnesium oxide, calcium oxide, bariumoxide, and mixtures of the foregoing. More specifically, the basicorganic or inorganic compound may be selected from the group consistingof: calcium carbonate, sodium carbonate, potassium carbonate, bariumcarbonate, sodium silicate, sodium borosilicate, magnesium oxide,strontium oxide, barium oxide, zeolites, sodium citrate, potassiumcitrate, calcium stearate, potassium stearate, sodium phosphate,potassium phosphate, magnesium phosphate, mixtures of silicone dioxidewith one or more of the following oxides: magnesium oxide, calciumoxide, barium oxide, and mixtures of one or more of the above.Furthermore, hydroxides of the metals and alkaline earth elementsrecited above may be utilized.

Where a basic inorganic odor suppressing compound is chosen, generallysuch compound is selected from the group consisting of calciumcarbonate, sodium carbonate, potassium carbonate, barium carbonate,aluminum oxide, sodium silicate, sodium borosilicate, magnesium oxide,strontium oxide, barium oxide, zeolites, sodium phosphate, potassiumphosphate, magnesium phosphate, mixtures of silicone dioxide with one ormore of the following oxides: magnesium oxide, calcium oxide, bariumoxide, and mixtures of one or more of the basic inorganic compounds setforth above. The amount of a basic inorganic compound is generally fromabout 2 to 20 weight percent, but is usually from about 5 to about 15weight percent of the article. Most preferably the basic inorganiccompound selected is calcium carbonate; typically present from about 5to about 20 weight percent.

Where an organic compound is chosen, it is typically selected from thegroup consisting of sodium stearate, calcium stearate, potassiumstearate, sodium citrate, potassium citrate, and mixtures of these wherethe amount of such compound is from about 0.5 to about 2.5 weightpercent of the article.

Typically, microwaveable articles produced in accordance with thepresent invention exhibit a relative aroma intensity index of less thanabout 1.0; preferably less than about 0.7; with a practical lower limitbeing 0.1 or so.

As shown below in connection with microwaveability testing, andsummarized in Table 20, competing commercial polystyrene type platescannot withstand the high temperatures generated in the microwave ovenduring food contact and either significantly warp or deform when theaforementioned food products were heated on them. Under the usualmicrowaving conditions with high grease content foods, the prior artplates tend to deform and flow to the point where parts of the platebecome adhered to the inside of the microwave oven. For disposableplates and containers, having suitable food contact olfactoryproperties, appearance and feel are important attributes. Themicronodular surface of the plates and containers of this inventionwhere mica and the basic inorganic compound or basic organic compoundare used in combination with polypropylene or polypropylene polyethylenecopolymers or blends tend to give these products the pleasingappearance, feel of stoneware or a pottery-like look and suitable foodcontact olfactory properties. Another significant property of thecontainers and plates of this invention is their cut resistance. Theserigid articles of manufacture are of sufficient toughness to beresistant to cutting by serrated polystyrene flateware. In normal usagethey are also resistant to cutting by regular metal flatware.

Whereas any microwaveable article may be produced in accordance with theinvention, most typically the article is a bowl or a plate suitable forserving food at a meal. The articles may be produced by injectionmolding; however, preferred articles are thermoformed and include amicronodular food contact surface. Micronodular food contact surfacesare produced by thermoforming a sheet into the article which has beenextruded optionally with at least one matte roll and by vacuumthermoforming the sheet by applying vacuum opposite to the surface wherethe micronodular surface is desired. Most typically the micronodularsurface will have a surface gloss of less than about 35 at 75° asmeasured by TAPPI method T480-OM 92. Articles also will typically have aParker Roughness Value of at least about 12 microns.

While any suitable polypropylene polymer may be used, the polypropylenepolymers are preferably selected from the group consisting of isotacticpolypropylene, and copolymers of propylene and ethylene wherein theethylene moiety is less than about 10% of the units making up thepolymer, and mixtures thereof. Generally, such polymers have a melt flowindex from about 0.3 to about 4, but most preferably the polymer isisotactic polypropylene with a melt-flow index of about 1.5. Inparticularly preferred embodiments, the melt compounded composition fromwhich the resultant extruded sheet is formed into articles furtherincludes a polyethylene component and titanium dioxide. The polyethylenecomponent may be any suitable polyethylene such as HDPE, LDPE, MDPE,LLDPE or mixtures thereof.

The various polyethylene polymers referred to herein are described atlength in the Encyclopedia of Polymer Science & Engineering (2d Ed.),Vol. 6; pp: 383-522, Wiley 1986; the disclosure of which is incorporatedherein by reference. HDPE refers to high density polyethylene which issubstantially linear and has a density of generally greater that 0.94 upto about 0.97 g/cc. LDPE refers to low density polyethylene which ischaracterized by relatively long chain branching and a density of about0.912 to about 0.925 g/cc. LLDPE or linear low density polyethylene ischaracterized by short chain branching and a density of from about 0.92to about 0.94 g/cc. Finally, intermediate density polyethylene (MDPE) ischaracterized by relatively low branching and a density of from about0.925 to about 0.94 g/cc. Unless otherwise indicated these terms havethe above meaning throughout the description which follows.

The microwaveable articles according to the invention typically exhibitmelting points from about 250 to about 330° F. and include mica inamounts from about 20 to about 35 weight percent. Most preferably micais present at about 30 weight percent.

It has been found that C8 and C9 organic ketones correlate well with orare associated with undesirable odors in polypropylene/micacompositions. Accordingly, it is preferred that articles in accordancewith the invention are substantially free from volatile C8 and C9organic ketones. In order to avoid undesirable odors, articles inaccordance with the invention are preferably prepared from a meltcompounded polyolefin mica composition which is prepared at a processmelt temperature of less than about 425° F.; with below about 400° F.being even more preferred. Optionally, the melt processedpolyolefin/mica composition is melt compounded in a nitrogen atmosphere.

In another aspect of the invention there is provided a microwaveable,disposable food contact article having food contact compatible olfactoryproperties formed of a melt processed polyolefin/mica compositionwherein said composition includes from about 40 to about 90 percent byweight of a polypropylene polymer and from about 10 to about 50 percentby weight mica and a basic organic or inorganic odor suppressingcompound including the reaction product of an alkali metal or analkaline earth element with carbonates, phosphates, carboxylic acids aswell as alkali metal and alkaline earth element oxides and silicates andbasic metal oxides, including mixtures of silicone dioxides with one ormore of the following oxides: magnesium oxide, calcium oxide, bariumoxide, and mixtures thereof.

Preferably the inventive articles are prepared from a melt compoundedpolyolefin/mica composition prepared by way of a low temperaturecompounding process.

A preferred low temperature compounding process used for producingpolypropylene/mica melt compounded compositions including a basic odorsuppressing agent having olfactory properties suitable for food contactapplications in accordance with the invention includes the sequentialsteps of: (a) preheating a polypropylene polymer while maintaining thepolymer below a maximum temperature of about 350° F. and more preferablybelow a maximum of about 260° F.; but suitably above about 240° F.;followed by; (b) admixing mica to said preheated polymer in an amountfrom about 10 to about 50 percent weight based on the combined weight ofthe resin and mica and maintaining the mixture below about 425° F.;followed by, (c) extruding the mixture. Polymer may be meltedexclusively through the application of shear, or the shear may besupplemented through heating by infrared radiation or ordinary heatingcoils or performed externally to the mixing chamber. Preferably, thebasic odor suppressing agent is added simultaneously with the mica.

It is desirable to keep the duration of the step of admixing mica and abasic odor suppressant agent to the mixture relatively short so as notto generate compounds which cause odor and to preserve the particle sizeand aspect ratio of the mica. Accordingly, the step of admixing the micashould be no more than about five minutes with the duration of theadmixing step of less than about three minutes being even morepreferred. Any suitable means may be used to carry out the sequentialprocess in accordance with the invention, however, the process isnormally carried out in a batch mode in a mixing chamber provided with apair of rotating rotors in an apparatus referred to in the industry as aBanbury type mixer. One may choose to use a twin screw extruder or aBuss kneader to practice the inventive process if so desired, providedthat appropriate elements are used to minimize shear heating.

In a further aspect of the invention, there is provided a process formaking pottery-like, micronodular, low-odor microwaveable containers.The inventive process is generally directed to a process for forming amicrowaveable, disposable, rigid and strong, mica and basic inorganic ororganic compound filled polyolefin containers having food contactcompatible olfactory properties, the polyolefin being selected from thegroup consisting of polypropylene and polypropylene polyethylenecopolymer or blend, and a mixture of these wherein the inorganic ororganic compound is selected from the group consisting of calciumcarbonate, sodium carbonate, potassium carbonate, barium carbonate,aluminum oxide, sodium silicate, sodium borosilicate, magnesium oxide,strontium oxide, barium oxide, zeolites, sodium phosphate, potassiumphosphate, magnesium phosphate, sodium stearate, calcium stearate,potassium stearate, sodium citrate, potassium citrate, hydroxides ofthese elements, and mixtures of these organic compounds, mixtures ofsilicon dioxide with one or more of the following oxides: magnesiumoxide, calcium oxide, barium oxide, and mixtures of one or more of thebasic inorganic or organic compounds set forth herein. The processinvolves the steps of:

(a) forming an extrudable admixture of the polyolefin resin, mica, andthe basic inorganic compound or basic organic compound;

(b) extruding the extrudable admixture of the polyolefin resin, mica,and the basic inorganic compound or the basic organic compound atelevated temperature;

(c) passing the resulting extruded admixture of the polyolefin resin andmica and the basic inorganic compound or the basic organic compoundthrough a multiple roll stack, at least one roll of said stack having amatte finish;

(d) thermoforming the extruded admixture of the polyolefin, resin, mica,and the basic inorganic compound or organic compound; and

(e) recovering a container having a micronodular surface and exhibitinga melting point of no less than 250° F.

The container is dimensionally stable and resistant to grease, sugar,and water at temperatures up to about 220° F. and has sufficienttoughness to be resistant to cutting by serrated flatware. The amount ofthe basic inorganic compound or basic organic compound added issufficient to reduce carbonyl moiety containing decomposition productsto provide containers with suitable food contact compatible olfactoryproperties.

The process most preferably includes:

(a) forming an extrudable admixture of the polyolefin resin, mica, andthe basic inorganic compound or basic organic compound;

(b) extruding the extrudable admixture of the polyolefin resin and micaand the basic inorganic compound or the basic organic compound atelevated temperature;

(c) passing the resulting extruded admixture of the polyolefin resin andmica and the basic inorganic compound or the basic organic compoundthrough a multiple roll stack, at least one roll of the stack having amatte finish;

(d) passing the extruded admixture of the polyolefin resin, mica, andbasic inorganic compound or the basic organic compound at leastpartially around the roll having a matte finish;

(e) controlling the speed of the extrusion process, the size,temperature and configuration of the roll stack such that the surface ofthe extruded admixture of the polyolefin resin, mica, and the basicinorganic or organic compound not in contact with the matte roll has acoarse-grained structure;

(f) thermoforming the extruded admixture of the polyolefin, resin, mica,and the basic inorganic compound or organic compound; and

(g) recovering a container having a micronodular surface and a roughsurface and exhibiting a melting point of no less than 250° F.

The coarse-grained structure of the surface of the extruded admixture ofthe polyolefin resin, mica, and the basic inorganic compound or basicorganic compound not in contact with said matte roll is formed bytransversing the extruded admixture of the polyolefin resin, mica, andthe basic inorganic compound or basic organic compound through acurvilinear path and at least partially solidifying the surface of theextruded admixture of polyolefin resin, mica, and the basic inorganiccompound or basic organic compound not contacting said matte roll whilethat surface is in tension relative to the surface contacting said matteroll. The container may be a plate, a cup, a bowl, a tray, a bucket, asouffle dish or the like.

Thermoforming is typically conducted at a sheet temperature of fromabout 260° to about 310° F., and more preferably at a temperature offrom about 280° to about 300° F.

There is provided in a still further aspect of the invention acrack-resistant, thermoformed food contact article having a wallthickness ranging from about 10 to about 80 mils consisting essentiallyof from about 40 to about 90 weight percent of a polypropylene polymer,from about 10 to about 50 percent by weight mica, from about 1 to about15 percent by weight polyethylene, from about 0.1 to about 5 weightpercent titanium dioxide and optionally including a basic organic orinorganic compound. The basic compound is, generally speaking, thereaction product of an alkali metal or alkaline earth element withcarbonates, phosphates, carboxylic acids as well as alkali metal andalkaline earth element oxides, hydroxides, or silicates and basic metaloxides, including mixtures of silicone dioxide with one or more of thefollowing oxides: magnesium oxide, calcium oxide, barium oxide, andmixtures thereof. A particularly preferred article is where the basicorganic or inorganic compound is calcium carbonate which is present inan amount of from about 5 to about 20 weight percent.

Polyethylene is more typically present from about 2.5 to about 15 weightpercent, preferably from about 4 to about 5 weight percent of the crackresistant article.

Titanium dioxide is included in various amounts, from about 0.1 to about3 percent by weight being typical; from about 0.25 to 2 percent titaniumdioxide may be included. Preferably, titanium dioxide is included in atleast 0.5 percent by weight.

The caliper, or wall thickness, of the articles is usually from about0.010 to about 0.050 inches or from about 10 mils to 50 mils. A caliperof from about 15 to 25 mils is most typically employed.

While any suitable polypropylene polymer may be employed, the mostpreferred polymer is isotactic polypropylene having a melt index in therange of from about 0.3 to 4, with a melt index of about 1.5 beingtypical. The polyethylene employed may be HDPE, LLDPE, LDPE or MDPE,mixtures thereof or a polyethylene with bimodal molecular weightdistribution. Polypropylene is sometimes referred to hereafter as “PP”.

The inventive compositions from which the crack resistant articles aremade do not include coupling agents such as maleic anhydride containingpolypropylene as further described herein, but may optionally includeother components which do not alter the basic and novel characteristicsof the crack-resistant plates. For example, nucleants such as sodiumbenzoate in amounts detrimental to crack resistance are to be avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given herein below and the accompanying drawings,which are given by way of illustration only, and thus, are notlimitative of the present invention and wherein:

FIG. 1 is a schematic flow diagram of the sheet extrusion process;

FIG. 2 is a schematic flow diagram of the thermoforming process for themanufacture of plates and containers having a micronodular surface;

FIG. 3 is a chrornatograph of a melt processed polypropylene/micacomposition exhibiting relatively high odor;

FIG. 4 is a chromatograph of a melt processed polypropylene/micacomposition exhibiting relatively low odor;

FIG. 5 is a plot of sensor responses vs. time for an automated aromascanning device;

FIG. 6 is a plot of the response integrals for the 32 sensors in anaroma scanning device for 3 different polypropylene/mica compositions;

FIG. 7 is a schematic diagram of a Banbury type compounder;

FIG. 8 is a plot of current draw vs. time for a compounding processaccording to the present invention in a compounder of the type shown inFIG. 7:

FIG. 9A is a scanning electron photomicrograph of a plate (upperpicture) and FIG. 9B is a scanning electron photomicrograph of a sheet(lower picture) of this invention wherein there is shown themicronodular food contact surface of the plate but not so for the neatextruded sheet;

FIG. 10 is a graph plotting gloss versus mica level;

FIG. 11 is a graph plotting the plate rigidity versus mica level;

FIG. 12A is a scanning electron photomicrograph of a sheet of thisinvention showing a matted surface and FIG. 12B is a scanning electronphotomicrograph of a non-matted surface;

FIGS. 13A and 13B are scanning electron photomicrographs of sheets ofthis invention showing two high gloss sides;

FIGS. 14A and B are isometric drawings of a plate of this invention;

FIGS. 15A through C include cross sectional views of the plate shown inFIGS. 14A and B;

FIG. 16 is a radial cross-section of the plate shown in FIGS. 14A and B;

FIG. 17 is a schematic profile of the plate shown in FIGS. 14A and B,beginning from the center line of the plate, formed in accordance withthe present invention;

FIG. 18 is a drawing of another plate of this invention;

FIG. 19 is a cross sectional view of the plate shown in FIG. 18;

FIG. 20 is a schematic profile of the plate shown in FIG. 18 beginningfrom the center line;

FIGS. 21A and 21B are drawings of a tray included in this invention;

FIGS. 22 A, B and C include a cross sectional view of the tray shown inFIGS. 21A and B;

FIG. 23 is a radial cross section of the tray shown in FIGS. 21A and B;

FIG. 24 is a schematic profile of the tray shown in FIGS. 21A and Bginning from the center line;

FIGS. 25A and B are drawings of a bowl of this invention;

FIGS. 26A through C include a cross-sectional view of the bowl shown inFIGS. 25A and B;

FIG. 27 is a radial cross section of the bowl shown in FIGS. 25A and B;

FIG. 28 is a schematic profile of the bowl shown in FIGS. 25A and Bbeginning from the center line;

FIG. 29 is a drawing of a take-out food container included in thisinvention;

FIGS. 30A and B are drawings of another bowl of this invention;

FIGS. 31A through 31C include a cross-sectional view of the bowl shownin FIGS. 30A and 30B;

FIG. 32 is a radial cross section of the bowl shown in FIGS. 30A and30B;

FIG. 33 is a profile of the bowl shown in FIGS. 30A and 30B;

FIG. 34 is a graph comparing the rigidity of the plates of thisinvention with prior art commercial products in the context of currentmaterial costs; and

FIG. 35 is a bar graph comparing the heat resistance of the plates ofthis invention with prior art commercial products.

DETAILED DESCRIPTION OF THE INVENTION

The aesthetically pleasing microwaveable disposable, rigid and strongcontainers including plates, bowls, cups, trays, buckets, soufflé dishesand lids comprise isotactic polypropylene, propylene-ethylene copolymer,or blends of isotactic polypropylene and propylene-ethylene copolymercoupled with a mixture of a platy inorganic mineral such as mica andbasic inorganic or organic compounds which are the reaction product ofan alkali metal or alkaline earth element with carbonates, hydroxides,phosphates, carboxylic acids, mixtures of silicon dioxide with one ormore of the following oxides: magnesium oxide, calcium oxide, bariumoxide, and mixtures of one or more of the basic organic or inorganiccompounds set forth herein.

Suitably the basic inorganic or organic compounds are selected from thegroup consisting of calcium carbonate, sodium carbonate, potassiumcarbonate, barium carbonate, sodium silicate, sodium borosilicate,magnesium oxide, strontium oxide, barium oxide, zeolites, sodiumphosphate, potassium phosphate, magnesium phosphate, mixtures of silicondioxide with one or more of the following oxides: magnesium oxide,calcium oxide, barium oxide, and mixtures of these or other basicinorganic or organic compounds such as sodium stearate, calciumstearate, potassium stearate, sodium citrate, potassium citrate, andmixtures of these basic organic compounds.

The function of the basic inorganic compound or organic compound is tominimize the formation of odor-causing compounds in the mica/polyolefincomposition and thus provide products with food contact compatibleolfactory properties for consumer use. In this connection, the amount ofthe basic inorganic compound or organic compound added is controlled tobe sufficient to reduce formation of decomposition products tosufficiently low levels to provide containers and plates with suitablefood contact compatible olfactory properties. Suitably 5 to 15 weightpercent of the container comprises the basic inorganic compound,advantageously about 8 to 12 percent. When the basic organic compoundsare used, lower quantities are required, suitably from about 0.5 to 2.5weight percent, advantageously 1.0 to 1.5 percent. Coupling agents andpigments may be utilized. Maleic anhydride and acrylic modifiedpolypropylenes are suitable coupling agents for some embodiments.

The containers, bowls, trays and plates of this invention are preferablyproduced by compounding a suitable resin/mica composition; forming itinto a sheet as shown in FIG. 1 and then thermoforming the sheet asshown in FIG. 2. These examples are illustrative and are not limitativeof a preferred commercial process which involves in-line extrusion withregrind and thermoforming with multi-cavity mold beds.

Advantageously, the sheet is formed by an extrusion process utilizingthe compounded polymer/mica basic inorganic compound or basic organiccompound mixtures. The final extrusion process renders a sheet withexcellent thermal properties, cut resistance, and food contactcompatible olfactory properties. Generally, injection molding isinherently not suitable for the manufacture of self-texturizedmicronodular containers, bowls, trays and plates, since injection moldedproducts are smooth plastic like articles which do not exhibit amicronodular surface or have the feel of stoneware or pottery-like look.

The aesthetically pleasing disposable microwaveable containers, trays,bowls and plates exhibit (a) food contact compatible olfactoryproperties, and (b) a melting point of at least 250° F. In addition, thecontainer or plate is dimensionally stable and resistant to grease,sugar, and water at temperatures of up to about 220° F. and are ofsufficient toughness to be resistant to cutting by serrated polystyreneflatware. The preferred mica and basic inorganic compound or the basicorganic compound filled polypropylene plates, besides exhibiting foodcontact compatible olfactory properties, exhibit on at least one side amicronodular surface and a thickness uniformity characterized by athickness coefficient of variation (COV) of less than about fivepercent.

Mica is a common name for naturally occurring inert mineral of thephyllosilicate chemical family, specifically potassium aluminosilicatewhereby the aluminum ions may be partially replaced by iron andmagnesium and part of the chemically bound water may be substituted byfluorine.

Mica is easily cleaved into thin, relatively regular, flexible yetstrong sheets (leaf-like flakes) with thickness in the range of half amicron and aspect ratio as high as 300. Mica is much softer than otherinorganic fillers (wollastonite, glass) yet only slightly harder thantalc. Mica has a slippery tactile feel and low abrasiveness relative toother common inorganic fillers.

The reinforcement effect at 40 weight percent mica is equivalent to thatof 30 weight percent glass fiber. Hard inorganic fibrous fillers such asglass (various lengths) and wollastonite (acicular structures) haveserious drawbacks such as abrasiveness and are prone to fracturedegradation during conventional melt processing. Other fibrous (organic)fillers are derived from wood and vegetable sources and are not suitablefor use in the manufacture of the containers of this invention since theorganic fillers, when used in substantial amounts, tend to degradeduring processing and they are also moisture sensitive. Preferably about20 to 35 weight percent mica are used.

In some applications it may be preferred to treat the mica and/or basicinorganic compounds prior to using them in the inventive articles. Asuitable compound for this treatment is amino-silane; sometimes referredto as a “coupling” agent.

Suitable basic inorganic and organic compounds used in the processinclude: calcium carbonate, sodium carbonate, sodium hydroxide,potassium carbonate, barium carbonate, aluminum oxide, sodium silicate,sodium borosilicate, magnesium oxide, strontium oxide, barium oxide,zeolites, sodium phosphate, potassium phosphate, magnesium phosphate,mixtures of silicon dioxide with one or more of the following oxides:magnesium oxide, calcium oxide, barium oxide, and mixtures of these orother basic inorganic or organic compounds such as sodium stearate,calcium stearate, potassium stearate, sodium citrate, potassium citrate,and mixtures of these basic compounds.

In the case where microwaveability is desired for a plastic disposablefood contact article, the not so perfect solution has been the use ofrelatively expensive high heat modified polystyrene based or heatresistant materials (e.g., unfilled PPO and SMA engineering resins),where PPO refers to polyphenylene oxide and SMA refers to styrene-maleicanhydride copolymer.

The mica and basic inorganic compound or basic organic compound filledpolypropylene containers, bowls, trays and plates of this invention haveovercome the disadvantages of the prior art type containers, bowls,trays and plates and are significantly superior to them.

Mica and the basic inorganic compound or the basic organic compoundfilled polypropylene is compounded by pre-blending the polypropylene inpellet or flake form with mica powder and the basic inorganic compoundor the basic organic compound powder and other additives (colorconcentrates, pigments, antioxidants, lubricants, nucleating agents,antistatic agents, etc.). This mixture is conveyed into the feed sectionaddition point of a twin screw compounding extruder, or compounded in aBanbury-type mixer to provide a melt-processed polyolefin composition.Alternatively, the components are advantageously fed separately into thesame or different points of addition, using combinations of volumetricand/or gravimetric (i.e., loss in weight type) feeders as furtherdescribed herein.

For white pigmentation, titanium dioxide is preferred due to combinationof brightness, and opacity, as well as stability during processing andfinal use. Surface treatment may be optionally used to further enhancewetting, dispersion, compatibility with matrix resins whereas thetitanium dioxide forms may be of the rutile or anatase type. Alternatewhite pigments may also consist of calcined clay or blends of calcinedclay with titanium dioxide. For black pigmentation, carbon black ispreferred due to a combination of desirable characteristics such asblackness, and dispersibility, the latter of which can be carefullycontrolled by choice of particle size and surface chemistry. Carbonblack is amorphous carbon in finely divided form which is made by eitherthe incomplete combustion of natural gas (channel black) or by reductionof liquid hydrocarbons in refractory chambers (furnace black).

A twin screw extruder provides sufficient mixing action to effectivelycause the wetting and dispersion of the filler into the polymer matrix.The twin screw extruder may be of the co-rotating or counter-rotatingtype, where each type is equipped with different screw flight elementswhich are appropriate for the feed, mixing, and melt metering zones. Thedischarge zone normally consists of a strand die where the exitingmolten material strands are quenched in a circulating water bathfollowed by knife cutting into pellets. In a particularly preferredembodiment, a Banbury-type mixer is used for compounding the resin, micaand basic compound as further described herein.

Low molecular weight additives such as waxes, fluorinated polymers, andother specialty lubricants are suitably used as process aids to reducethe melt viscosity and improve throughput. Polyethlene resin may also beadded to the blend. Other additives may include nucleating agents andantistatic agents. Antioxidants may be added in small amounts, generallyless than one weight percent, to minimize shear and thermal degradationof the polypropylene during the extrusion and forming processes as wellas to promote the chemical stability of the sheet prior to and duringfinal article use. Suitable antioxidants are advantageously selectedfrom the group of phenolics and phosphites and blends thereof. These areproduced by Ciba-Geigy and General Electric Corporation.

Plastic sheet extrusion equipment is suitable for the manufacture ofmultilayered or single layered mica and the basic inorganic or organiccompound filled sheets of a polyolefin selected from the groupconsisting of polypropylene, polypropylene/polyethylene copolymer orblend, and mixtures of these. Melt strength of the sheets is improvedwhen mica is used as a filler since geometry of the mineral in the formof high aspect ratio flakes serves to provide “inter-particleconnectivity” or physical cross-linking. The food contact compatibleolfactory properties are enhanced when in addition to the mica, basicinorganic compounds or organic compounds such as calcium carbonate,sodium carbonate, potassium carbonate, barium carbonate, sodiumsilicate, sodium borosilicate, magnesium oxide, strontium oxide, bariumoxide, zeolites, sodium phosphate, potassium phosphate, magnesiumphosphate, mixtures of silicon dioxide with one or more of the followingoxides: magnesium oxide, calcium oxide, barium oxide, and mixtures ofthese or other basic inorganic or organic compounds such as sodiumstearate, calcium stearate, potassium stearate, sodium citrate,potassium citrate, and mixtures of these are mixed with mica and thepolyolefin to produce the containers of this invention.

In FIG. 1 a process is shown for the manufacture of a single layer micafilled polypropylene sheet or polypropylene filled with mica and basicinorganic compounds or organic compounds set forth hereinabove.Previously compounded and pelletized mixtures of polypropylene, mica andthe basic inorganic compound or organic compound, and other additivesare gravity fed by a hopper 10 into the feed zone of a single screwextruder system. Primary extruder 11 has a 2 inch diameter screw with a24/1 length to diameter ratio. Optionally multilayer coextruded sheetcan be produced by utilizing at least one additional single screwextruder 12,13,14 in conjunction with a combining feedblock with propermelt piping and manifold arrangements. Suitably one to seven screwextruders are employed, preferably three. A flexible lip flat sheet die15 having a width of 31 inches was used.

The sheet of this invention 16 enters the sheet takeoff portion (i.e.,after the molten material exits the die) compromising a three-rollpolishing/casting unit 17 with individually temperature controlledrolls, a two-rubber roll sheet pull unit 18, and a dual turret, dualshaft winder, whereby only one shaft winder roll 19 may be used. Thethree takeoff units were mechanically tied together, were on a commontrack, and can be automatically traversed from close die lip proximityto about 36 inch distant. During the extrusion process, the distancebetween the die exit and the casting unit was maintained at 2 inches.These three chrome rolls comprising the sheet casting unit areindividually temperature controlled by integral oil circulating pumpsand heat exchangers. Nip gaps are adjustable. A speed differentialbetween cast rolls and pull rolls is normally maintained such that pullroll speed is approximately within ten percent (10%) of cast roll speed.On a pilot line, achievable line speeds are in the range of 1-12.5 feetper minute; while for a sheet on the order of 20 mil thick, the linespeed is about 5-6 feet per minute. The sheet is wound on a roll 19.Table 1 shows the sheet process conditions employed for the sheetextrusion of mica and basic inorganic compound or the basic organiccompound filled polypropylene and the unfilled polypropylene control. Ina commercial operation, the speed is increased by a factor of 10 to 20times.

Thermoforming is the pressing or squeezing of pliable material intofinal shape. In the simplest form, thermoforming is the draping of asoftened sheet over a shaped mold. In the more advanced form,thermoforming is the automatic, high speed positioning of a sheet havingan accurately controlled temperature into a pneumatically actuatedforming station whereby the article's shape is defined by the mold,followed by trimming and regrind collection.

Forming techniques other than conventional thermoforming are alsosuitable for the manufacture of articles described in the presentinvention. These include variations such as presoftening the extrudedsheet to temperatures below the final melting temperature, cutting flatregions (i.e., blanks) from the sheet, transfer of blanks by gravity ormechanical means into matched molds whereby the blanks are shaped intothe article by heat and pressure. The sheet from which the blanks havebeen cut out is collected as regrind and is recyclable. Conventionalpaperboard pressing equipment and corresponding forming tooling isoptionally modified to produce articles of this invention.

The extruded sheet used in a preferred thermoforming process as shown inFIG. 2 has a thickness of about 0.010 to 0.080 inches (10 to 80 mils),suitably 0.010 to 0.050 inches. For the plates the preferred thicknessis about 0.015 to 0.025 inches. Suitable mica filler loading level inthe extruded sheet is in the range of 10 to 50 weight percent, morepreferably 20-50 weight percent and most preferably 20-35 weightpercent. To achieve suitable food contact compatible olfactoryproperties, the basic inorganic compound loading level should be 5 to 15weight percent, advantageously 8 to 12 weight percent. For the basicorganic compound the loading levels should be 0.5 to 2.5 weight percent,preferably 1.0 to 1.5 weight percent. The mica flake aspect ratio is inthe range of 30-300, more preferably 15-250, with particle size range ofabout 10-500 microns. The extruded sheet comprises isotacticpolypropylene homopolymer or polypropylene polyethylene copolymer orblend or a mixture of these as base resin, preferably having a melt flowindex in the range from about 0.3 to about 4.0, more preferably 0.5-2.0and most preferably about 1.5. Propylene copolymers or blends withethylene levels in the range of 1-10 mole percent, more preferably 2-5mole percent, are optionally used.

The preferred type of mica is muscovite, which is the most common formin commerce. Optionally other less common mica types such as phlogopite,biotite and fluorphlogopite are used. Although there are an infinitenumber of compositions possible for these four generic types due toisomorphous substitution which are mine specific, the selection ofparticular grades is driven by particle aspect ratio, particle size,price and availability.

Suitably the extruded sheet includes coloring agents for aestheticappeal, preferably titanium dioxide, carbon black, and other opacifyingagents in the range of 0.5-8 weight percent based on total composition,preferably 1.5 to 6.5 weight percent. The extruded sheet comprises minoramounts of other additives such as lubricants and antioxidants. Thesearticles of manufacture may be suitably colored with pigments or dyes.Pigments are defined as small insoluble organic or inorganic particlesdispersed in the resin medium to promote opacity or translucency. Usualpigments include carbon black, titanium dioxide, zinc oxide, ironoxides, and mixed metal oxides. Dyes are organic and soluble in theplastic, and may be used alone or in combination with pigments tobrighten up pigment based colors. All such colorants may be used in avariety of modes which include dry color, conventional colorconcentrates, liquid color and precolored resin.

Mica and the basic inorganic compound or the basic organic compoundfilled polypropylene sheets are suitably formed into plates, bowls,cups, trays, buckets, souffle dishes, and containers using a forming orthermoforming process disclosed herein. In a pilot process, thesearticles of manufacture and containers may be made using the CometStarlett thermoformer unit. This machine is capable of vacuum formingproducts from heat softened thermoplastic materials and is schematicallydepicted in FIG. 2. Sheet portions 23 having dimensions of 17.5 inchesby 16.25 inches were clamped on two opposing sides and inserted into anoven indicated at 22 equipped with upper 20 and lower 21 heaters,whereby heater input settings were in the range of 20-30 percent andhold times were on the order of 60-80 seconds. Under these conditions,the oven air temperature as recorded by a digital thermocouple was inthe range of 221° F. to 225° F., while the sheet surface temperature, asrecorded by adhering indicator thermocouples, was approximately 330° F.to 340° F.

When the clamped and heat softened sheet 23 exits the oven 22, it may bevacuum formed by either procedure (A) or (B) in a commercial process.Both methods utilize only one mold which is suitably fabricated fromepoxy thermoset materials or suitable mold materials including aluminum,steel, beryllium, copper and the like. Mode (A) uses a male mold 24whereby the sheet is sucked up to conform to it by means of vacuum wherethe vacuum ports are present on the mold base as well as on theperiphery side of the container (i.e., flange area). Mode (B)arrangement is such that the vacuum direction is opposite to mode (A),where again vacuum holes are located around the base and periphery . Inthe case of mode (B), a female mold 25 is used, and this arrangement ispreferred since the air side of the sheet corresponds to the foodcontact side. In mode (B) the food contact side undergoes a beneficialtexturizing effect as a result of the heat treatment, whereby the resinflows around and outward from the mica particles close to the surfacecausing the mineral to become more exposed which creates a micronodularsurface as manifested by decreased gloss and increased surfaceroughness. The micronodular surface gives the container a stoneware orpottery-like appearance.

Suitably a process for forming a disposable, microwaveable, rigid andstrong mica and the basic inorganic compound or the basic organiccompound filled polyolefin container, plate, bucket, or the like, havingfood contact compatible, olfactory properties wherein the polyolefin isselected from polypropylene, polypropylene polyethylene copolymer orblend and the basic inorganic compound and the basic organic compound isselected from the group consisting of calcium carbonate, sodiumcarbonate, potassium carbonate, barium carbonate, aluminum oxide, sodiumsilicate, sodium borosilicate, magnesium oxide, strontium oxide, bariumoxide, zeolites, sodium phosphate, potassium phosphate, magnesiumphosphate, mixtures of silicon dioxide with one or more of the followingoxides: magnesium oxide, calcium oxide, barium oxide, and mixtures ofthese or other basic inorganic or organic compounds such as sodiumstearate, calcium stearate, potassium stearate, sodium citrate,potassium citrate and mixtures of these comprise the steps of:

(a) forming an extrudable admixture of the polyolefin resin, mica, andthe basic inorganic compound or the basic organic compound;

(b) extruding said extrudable admixture of the polyolefin resin, micaand the basic inorganic compound or the basic organic compound atelevated temperature;

(c) passing the resulting extruded admixture of the polyolefin resin,mica and the basic inorganic compound or the basic organic compoundthrough a multiple roll stack, at least one roll of said stack having amatte finish;

(d) passing said extruded admixture of the polyolefin resin and mica andthe basic inorganic compound or the basic organic compound at leastpartially around said roll having a matte finish;

(e) controlling the speed of said extrusion process, the size,temperature and configuration of said roll stack such that the surfaceof said extruded admixture of polyolefin resin, mica and the basicinorganic compound or the basic organic compound not in contact withsaid matte roll has a coarse-grained structure; and

(f) thermoforming said extruded admixture of polyolefm, mica and thebasic inorganic compound or the basic organic compound and recovering acontainer, plate, bucket, or the like, having a micronodular surface anda rough surface, exhibiting a melting point of no less than about 250°F.; the container, plate, bucket, etc., being dimensionally stable andresistant to grease, sugar and water at temperatures up to about 220° F.and having sufficient toughness to be resistant to cutting by serratedflatware and exhibiting food contact compatible olfactory properties.

Advantageously, the coarse-grained structure of the surface of saidextruded admixture of polyolefm resin, mica and the basic inorganiccompound or the basic organic compound not in contact with said matteroll is formed by transversing the extruded admixture of the polyolefmresin, mica and the basic inorganic compound or the basic organiccompound through a curvilinear path and at least partially solidifyingthe surface of said extruded admixture of polyolefm resin, mica and thebasic inorganic compound or the basic organic compound not contactingsaid matte roll while that surface is in tension relative to the surfacecontacting the matte roll.

Generally, a process for forming a mica basic inorganic compound orbasic organic compound filled polypropylene container, plate, bucket,tray, bowl, or the like, comprises the steps of:

(a) forming an extrudable admixture of the polypropylene resin, mica andthe basic inorganic compound or the basic organic compound;

(b) extruding said extrudable admixture of the polypropylene resin, micaand the basic inorganic compound or the basic organic compound atelevated temperature;

(c) passing the resulting extruded admixture of the polypropylene resin,mica and the basic inorganic or the basic organic compound through amultiple roll stack, at least one roll of said roll stack having a mattefinish;

(d) passing said extruded admixture of the polypropylene resin, mica andthe basic inorganic compound or the basic organic compound at leastpartially around said roll having a matte finish;

(e) controlling the speed of said extrusion process, the size,temperature and configuration of said roll stack such that the surfaceof said extruded admixture of the polypropylene resin, mica and thebasic inorganic compound or the basic organic compound in contact withsaid matte roll has a matted structure; and

(f) thermoforming said extruded admixture of polypropylene resin, themica and the basic inorganic compound or the basic organic compound, andrecovering a container, plate, bucket, or the like having a micronodularsurface and exhibiting a melting point of no less that 250° F., thecontainer, plate, bucket, or the like being dimensionally stable andresistant to grease, sugar and water at temperatures up to about 220° F.and having sufficient toughness to be resistant to cutting by serratedflatware and further exhibiting food contact compatible olfactoryproperties.

A process for forming a mica and the basic inorganic compound or thebasic organic compound filled polypropylene sheet suitable forthermoforming micronodular containers and plates comprises the steps of:

(a) forming an extrudable admixture of the polypropylene resin, mica andthe basic inorganic compound or the basic organic compound;

(b) extruding said extrudable admixture of the polypropylene resin, micaand the basic inorganic compound or the basic organic compound atelevated temperature;

(c) passing the resulting extruded admixture of the polypropylene resin,mica and the basic inorganic compound or the basic organic compoundthrough a multiple roll stack, at least one roll of said roll stackhaving a matte finish;

(d) passing said extruded admixture of the polypropylene resin, mica andthe basic inorganic compound or the basic organic compound at leastpartially around said roll having a matte finish;

(e) controlling the speed of said extrusion process, the size,temperature and configuration of said roll stack such that the surfaceof said extruded admixture of the polypropylene resin, mica and thebasic inorganic compound or the basic organic compound not in contactwith said matte roll has a coarse structure; and

(f) the surface in contact with the matte roll has a matte surface; and

(g) recovering a sheet having a matted surface and a coarse surface,said sheet comprising polypropylene, mica and the basic inorganiccompound or the basic organic compound moieties. The sheet has foodcontact compatible olfactory properties.

Advantageously, other thermoforming arrangements are suitable and may bepreferred in conventional sheet and web feed thermoforming commercialproduction operations. Alternative arrangements include the use ofdrape, vacuum, pressure, free blowing, matched die, billow drape, vacuumsnap-back, billow vacuum, plug assist vacuum, plug assist pressure,pressure reverse draw with plug assist vacuum, reverse draw with plugassist, pressure bubble immersion, trapped sheet, slip, diaphragm,twin-sheet cut sheet, twin-sheet rollfed forming or any suitablecombinations of the above. Details are provided in J. L. Throne's book,Thermoforming, published in 1987 by Coulthard. Pages 21 through 29 ofthat book are incorporated herein by reference. Suitable alternatearrangements also include a pillow forming technique which creates apositive air pressure between two heat softened sheets to inflate themagainst a clamped male/female mold system to produce a hollow product.Metal molds are etched with patterns ranging from fine to coarse inorder to simulate a natural or grain like texturized look. Suitablyformed articles are trimmed in line with a cutting die and regrind isoptionally reused since the material is thermoplastic in nature. Otherarrangements for productivity enhancements include the simultaneousforming of multiple articles with multiple dies in order to maximizethroughput and minimize scrap.

Various measurements used herein include melt flow index, SSI rigidity(sometimes referred to below as simply “rigidity”), Parker Roughness andso forth. Unless otherwise indicated explicitly or by context, theseterms have the meaning set forth below.

The melt flow rate (MFR) or melt index is a common and simple method fordetermining the flow properties of molten polymers. (As used herein,ASTM D 1238-95, Condition 230/2.16). Resin is introduced and melted in acylindrical space. After temperature equilibration is reached, a weightis used to push a plunger vertically downward whereby the resin isextruded through a narrow orifice. The usual test temperature and thetemperature utilized herein for polypropylene is 230° C. and the load is2.16 Kg. Extruded material is collected and weighed and the timerequired to extrude a specific weight is recorded. MFR or melt index isexpressed as grams per minutes, or grams per 10 minutes, which is theweight of material extruded in a 10 minute time period. MFR is inverselyproportional to both polymer viscosity and polymer molecular weight.

SSI rigidity is measured with the Single Service Institute PlateRigidity Tester originally available through Single Service Institute,1025 Connecticut Ave., NW. Washington, D.C. The SSI Rigidity testapparatus has been manufactured and sold through Sherwood Tool, Inc.,Kensington, CT. This test is designed to measure the rigidity (i.e.resistance to buckling and bending) of paper and plastic plates, bowls,dishes, and trays by measuring the force required to deflect the rim ofthese products a distance of 0.5 inch while the product is supported atits geometric center. Specifically, the plate specimen is restrained byan adjustable bar on one side and is center fulcrum supported. The rimor flange side opposite to the restrained side is subjected to 0.5 inchdeflection by means of a motorized cam assembly equipped with a loadcell, and the force (grams) is recorded. SSI rigidity is expressed asgrams per 0.5 inch deflection. A higher SSI value is desirable sincethis indicates a more rigid product. All measurements were done at roomtemperature and geometric mean averages for the machine and crossmachine direction are reported.

The Parker Roughness method was used to determine roughness using theMessmer Parker Print-Surf Roughness. Operation procedure details arereferenced in the Messmer Instruments Ltd. User manual for theinstrument (Model No. ME-90) which is distributed by Huygen Corporation.The flat specimen is clamped under 1 Mpa pressure against a narrowannular surface by a soft backing and the resistance of air flow of thegap between the specimen and the annulus is measured. The air flow isproportional to the cube of the gap width and the roughness is expressedas the root mean cube gap in units of micrometers. Higher Parkerroughness values indicate higher degrees of surface roughness.

Gloss is reported as “gloss units at 75 or 60 degrees.” Glossmeasurements were conducted following TAPPI Standard Method T-480-OM 92.

The following examples are illustrative of the present invention. Itshould be understood that the examples are not intended to limit theinvention and that various modifications may be made by those skilled inthe art without changing the essential characteristics of the invention.

EXAMPLES 1-8

Mica filled polypropylene sheets (20 mil) and unfilled polypropylenesheets (22 mil) were extruded, as shown and described in connection within FIG. 1, with conditions specified in Table 1. These extrusion processconditions may be varied as necessary to produce sheets which are ofacceptable quality. Specifically, the operable temperature ranges forbarrel zones 1,2, and 3 are about respectively, 350 to 425° F., and 450to 500° F. the adaptor, feedblock, and die temperatures can all be inabout the range of 450 to 500° F. the range of values for extruder driveamperes, extruder speed, melt pressure, die pressure, chill rolltemperature, and line speed are about respectively, 12 to 20 amp., 60 to100 RPM, 1500 to 2500 psi, 450 to 650 psi, 120 to 140° F., and 3 to 8FPM. Sheets are subsequently vacuum thermoformed into plates and othercontainers and lids as set forth in FIGS. 14 through 33. There isreported in Tables 2 and 3, respectively, rigidity values and caliperdata for the sidewall, bottom, and flange rim) areas of vacuum formedplates using condition (B) of FIG. 2 and having a diameter of 10.25inches. In each table, individual rigidity values are shown for eachspecimen. In addition, the caliper uniformity for sidewall, bottom, andflange areas are reported for each specimen, along with the summarystatistics. Specifically, the caliper of each plate specimen in Tables 2and 3 was measured ten times using a Fowler gauge for each of the threeregions of interest consisting of the sidewall, bottom, and flangeareas, and the average value for each plate specimen is reported alongwith the corresponding standard deviation in thousands of inches or mils(i.e., individual plate statistics). In the case of the three plates ofTable 2, the caliper summary statistics (expressed in the averageproperties row) were obtained on the basis of averaging 30 measurements,wherein the standard deviation is reported for each of the three regionsof interest. In the case of the five plates of Table 3, the calipersummary statistics were calculated on the basis of averaging 50measurements where again the standard deviation is reported for each ofthe three regions of interest. Therefore, the caliper data of Tables 2and 3 located in the average property rows pertain to global statisticsrather than individual plate statistics. The caliper uniformityparameter consists of the coefficient of variation (COV) which iscalculated as the standard deviation of caliper divided by the meancaliper, whereas the ratio is multiplied by 100, whereas the abovedescribed global averages and associated standard deviations areemployed. A lower COV value is desirable since it signifies improvedcaliper uniformity for mica filled polypropylene plates with respect tounfilled polypropylene plates. Tables 2 and 3 show that mica reduces COVof polypropylene from 9.9 to 4.3 in sidewall and from 9.6 to 2.0 in theflange area. Therefore, caliper uniformity in sidewall improved by morethan a factor of 2 and caliper uniformity in the flange improved by overa factor of 4. The improvement of caliper uniformity is critical forpromoting plate dimensional stability during food transport andmicrowave cooking operations. In great contrast to mica filledpolypropylene plates, the unfilled polypropylene plates exhibited poorquality as evidenced by poorly defined rim area, and sharkskin, veryrough surface. These data demonstrate that mica greatly improves thedrawability of polypropylene as evidenced by improved caliperuniformity, as well as improved thermoformability, both of which are dueto enhanced melt strength relative to unfilled polypropylene. Mica isthe preferred reinforcing mineral filler for enhancing the melt strengthbecause of its highly regular, high aspect ratio morphology which can bethought of as resulting in “inter-particle connectivity” or “physicalcross-linking”. The significant reinforcing effect of mica is alsoevidenced by a SSI plate rigidity value of 671 grams per 0.5 inches forPP/mica at a basis weight of about 350 lbs. per square foot ream versus342 grams per 0.5 inches for unfilled PP at a basis weight of about 280lbs. per 3000 square foot ream.

TABLE 1 Sheet Extrusion Conditions for Mica Filled Polypropylene andUnfilled Polypropylene CONDITION PP/MICA UNFILLED PP Barrel Zone 1 (°F.) 395 395 Barrel Zone 2 (° F.) 425 425 Barrel Zone 3 (° F.) 475 475Adaptor (° F.) 470 450 Feed block (° F.) 470 460 Die Zones 1-3 (° F.)470 475 Extruder RPM 80 70 Drive amperes 16 19 Melt pressure (psi) 17001780 Die pressure (psi) 550 825 Line speed (FPM) 6.1 5.0 Chill rolltemp. (° F.) 130 137

TABLE 2 Caliper and Rigidity Data for 10-¼ Inch Plates Thermoformed FromUnfilled Polypropylene Sheet Plate Speci- men Ex- Rigidity SidewallBottom Caliper Flange ample (g/0.5 in.) Caliper (mil) (mil) Caliper(mil) 1 364 18.7 ± 1.9 20.7 ± 0.8 22.9 ± 2.8 COV* 10.1 3.9 12.2 2 38219.2 ± 20. 20.6 ± 0.4 23.3 ± 0.8 COV 10.4 1.9  3.4 3 280 19.6 ± 1.9 20.6± 0.5 23.3 ± 2.8 COV  9.7 2.4 12.0 Average 342 ± 54.4 19.19 ± 20.64 ±23.15 ± 2.21 Proper- 1.89 0.58 ties COV   9.85  2.81   9.55 COV =Coefficient of Variation

TABLE 3 Caliper and Rigidity Data for 10-¼ inch Plates Thermoformed FromPolypropylene/Mica/TiO₂ Sheet Plate Specimen Rigidity Sidewall BottomFlange Example (g/0.5 in.) Caliper (mil) Caliper (mil) Caliper (mil) 4705 18.3 ± 1.1 17.4 ± .05 18.2 ± 1.0 COV* 6.0 2.9 5.5 5 659 17.0 ± 1.517.9 ± 0.7 18.4 ± 0.5 COV 8.8 3.9 2.7 6 654 17.3 ± 1.6 17.0 ± 0.6 18.2 ±0.7 COV 9.2 3.5 3.8 7 669 16.9 ± 1.2 16.7 ± 1.1 18.9 ± 0.8 COV 7.1 6.64.2 8 668 16.3 ± 1.0 16.3 ± 0.9 19.0 ± 0.9 COV 6.1 5.5 4.7 Average 671 ±20  17.3 ± 0.76 17.1 ± 0.6 18.5 ± 0.38 Properties COV 4.3 3.5 2.0 COV =Coefficient of Variation

EXAMPLES 9-11

Thirty percent mica and ten percent calcium carbonate filledpolypropylene sheet was run on a commercial extrusion line. The extruderwas a 6″ Egan single screw with an EDI flex lip die. In these Examples9-11, the resulting melt temperature was approximately 400° F. and thetemperature for Barrel Zones 1-5 were approximately 400/396, 390/390,370/370, 370/370, and 370/371 as shown in Table 4.

Lower melt temperatures are typically preferred. Process melttemperatures of 370° F. or so will help control undesirable odors in theproduct. Process melt temperature as used throughout refers to ameasured value of the temperature of a composition when thepolypropylene is molten and unless otherwise stated, is indicative ofthe maximum temperature of a particular step.

For the runs reported in Table 4, an auger feeder was installed justabove the feed throat of the extruder to introduce color concentratesfor producing green, blue, and eggshell colored sheet. The concentratewas added at levels between 1%- 5%.

TABLE 4 Extrusion Conditions for 30% Mica/10% Calcium Carbonate FilledPolypropylene Set/Actual Conditions Green Blue Eggshell Barrel Zone 1Temp 400/396 400/398 400/399 (F.) Barrel Zone 2 Temp 390/390 390/390390/391 (F.) Barrel Zone 3 Temp 370/370 370/370 370/370 (F.) Barrel Zone4 Temp 370/370 370/370 370/370 (F.) Barrel Zone 5 Temp 370/371 370/370370/370 (F.) Adaptor Temp (F.) 370 370 370 Melt Temp (F.) 400 400-405404/405 Die Zone 1 Temp (F.) 380 385 385 Die Zone 2 Temp (F.) 370 370370 Die Zone 3 Temp (F.) 370 370 370 Die Zone 4 Temp (F.) 370 370 370Die Zone 5 Temp (F.) 380 385 385 Screw RPM 30 30 30 Drive Amperes325-345 335-352 347-350 Screen Pack 20 mesh 20 mesh 20 mesh BackPressure (psi) 2350-2510 2370-2600 2515-2680 Line Speed (fpm) 30/28/2030/28/22 27/26/20 Throughput (lb./hr.) 725 725 725 Top Stack Roll120-130 120-130 120-130 Temp (F.) Middle Stack Roll 120-130 120-130120-130 Temp (F.) Bottom Stack Roll 120-130 120-130 120-130 Temp (F.)Roll Gap-top (mil) 17 17 17 Roll Gap-bottom (mil) 23 23 23 Nip RollPressure 50 80 80 Die Gap (mil) 15 middle-30 15 middle-30 15 middle-30edges edges edges Die-Full Width (in) 52 52 52 Die to Nip DistanceApproximately Approximately Approximately (in) 4.5 4.5 4.5 Sheet Width(in) 51.5 51.5 51.5 Sheet Caliper (mil) 17.5/18.5/24 17.5/18.5/2417.5/18/24 Color Auger Setting 4 4 1 (%) Trim Regrind Used Yes Yes NoFootage Produced 12000 11000 15000

EXAMPLES 12-17 Aroma Profile Test Method

The Sensory Analysis Center at Kansas State University has developed aprofiling protocol in which a highly trained panel identifies specificodors and rates their intensity. The intensity scale is a 15-point“universal” scale of the type typically chosen for sensory studies,where 1 is barely perceptible or threshold and 15 is extremely strong.If an attribute or odor component is not listed in the tables whichfollow, it means it is not present and would score a 0. The panelmembers are selected on the basis of a series of screening tests thatinclude basic taste, odor recognition, taste intensity recognition,taste intensity ranking, and a personal interview to evaluateavailability and personality traits. Training, which includes thefundamental sensory principles and all aspects of the profile technique,is done over a 4-12 month period.

The panelists work as a group to arrive at a description of the product.Individual results are compiled by the panel leader and discussionfollows in which disagreements are discussed until a consensus isreached on each component of the profile. Reference materials and morethan one session usually are required in order to reach the consensus.

The procedure for resin is to place 40 ml. of resin in a 340 ml. glassbrandy snifter, which is covered with a watch glass. Sheet samples arecut into two 2″×2″ sections and placed in the same size brandy snifter.In testing, panelists found that some samples had initial odorcomponents that disappeared rapidly. Therefore an initial impact and asustained impact were evaluated for each sample. The initial impact wasjudged immediately after the watch glass had been removed; the sustainedimpact was judged 10 seconds after the watch glass had been removed.Typical results are shown in the Table 5 below for Low Odor and HighOdor Compostions. “Low” odor formulations were produced using lower meltprocessing temperatures in compounding and adding 10% calcium carbonateto the formulation. The sheets were prepared as shown and described inconnection with Examples 1 through 11.

TABLE 5 High Odor vs. Low Odor Polypropylene Composites: Effect ofAdding 10% CaCO₃ ODOR PROFILE FOR COMPOUNDED RESIN Resin ImpactConsensus Odor Profile on Resin (Kansas State University SensoryAnalysis Center) Resin Initial Sustained Petroleum Pungent MustyScorched Medicinal Sweet Waxy Soapy High Odor 9.0 3.5 8.0 4.0 7.0 3.53.0 Low Odor 5.5 2.5 2.5 4.5 1.5 2.0 4.5 High Odor Resin Low Odor Resin65.63% Polypropylene 55.63% Polypropylene 30% Mica 30% Mica 2.5%Coupling Agent 10% CaCO₃ 1.87% Pigment 2.5% Coupling Agent 1.87% Pigment

High Odor and Low Odor compositions were compounded utilizing theprocess melt temperatures indicated in the first column of Table 6 andformed into sheets as described above. Both resin and sheet wereevaluated for aroma profile.

TABLE 6 ODOR PROFILE FOR SHEET FORMED FROM COMPOUNDED RESIN AT TWOTEMPERATURES Sheet Impact Consensus Odor Profile on Sheet Resin InitialSustained Petroleum Pungent Musty Scorched Medicinal Sweet Waxy SoapyHigh Odor 370° F. 12.0 60 10.0 8.0 7.5 4.5 4.0 High odor 459° F. 11.0 807.5 7.5 6.0 3.5 2.0 Low Odor 371° F. 5.5 20 3.5 4.0 2.0 2.5 2.5 Low Odor460° F. 5.5 20 3.0 3.5 2.0 3.5

The foregoing data demonstrates that: when a basic moiety containingcompound was added to the mica polyolefin composition, a resin wasproduced having suitable food contact compatible olfactory properties.Significant decreases in the initial and sustained odors were observedand the scorched, pungent, and petroleum aroma components were removedor greatly reduced and these undesirable components seem to be replacedwith sweet, waxy, and soapy aroma components.

When compounded pellets are subjected to sheet extrusion, those withoutcalcium carbonate increase in the disagreeable components (pungent andpetroleum) and increase in the initial and sustained odor output withsubsequent processing. In contrast, when pellets contain calciumcarbonate, no increase in undesirable aroma components was observed andno increase in the initial or sustained odor was produced withsubsequent processing. Test panel data correlated well with analyticaltechniques as can be seen from the discussion and examples which follow.

C8/C9 Ketones

The precise nature of the odor causing compounds in polypropylene/micacompositions is not known; however, it has been found that undesirableodors correlate well with eight carbon (C8) and nine carbon (C9) alkylketones as described hereinafter, and may be associated with suchcompounds.

A Likens-Nickerson steam/methylene chloride extraction technique wasused to extract possible odor causing compounds from polypropylene/micacompositions and produce a concentrate. The extraction was performeduntil complete. The concentrate was analyzed through gaschromatography/mass spectrometry to produce chromatograms such as thoseshown in FIGS. 3 and 4. The abscissa is an arbitrary time scale, whilethe ordinate is an arbitrary abundance scale. The peak for alkyl C8(labeled as A) ketone assigned to be 4-methyl-2-heptanone, appears onboth FIGS. 3 and 4 at slightly above 16.8 on the time scale asindicated; while the peak for C9 alkyl ketone (labeled as B), assignedto be 4,6-dimethyl-2-heptanone appears slightly below 17.6 on the timescale in both chromatograms. Other peaks of interest on FIGS. 3 and 4are C7 ketones at slightly above 15.1, 15.6 and 16.3 on the abscissa.The peaks are respectively assigned to be 2-heptanone, 3-heptanone and4-heptanone. They are respectively labeled as C, D and E. There is alsoshown on both FIGS. 3 and 4 peaks for what are to be assigned to bevarious C7 alcohols at about 18, 18.2 and 18.8 on the abscissa. Thesecompounds are respectively labeled as F, G and H on the diagrams and areassigned to be 2-heptanol, 3-heptanol, and 4-heptanol. The C8/C7 ratiosreferred to hereinafter are ratios of the abundance at the peaksassigned to be 4-methyl-2-heptanone to the abundance at the peakassigned to be 4-heptanone as measured by Likens-Nickerson extractionfollowed by gas chromtography/mass spectrometry. That is, the C8/C7ratio for a given sample is the ratio of peak intensity (height) of peakA to the peak intensity of peak E. Similarly, the C9/C7 ratio is theratio of the peak intensity of peak B to the peak intensity of peak E inFIGS. 3 and 4 for a given sample.

FIG. 3 is a chromatogram characteristic of extruded pellets having arelatively strong odor wherein the C8 and C9 ketones indicated each havean extractable concentration of about 10 parts per million parts byweight in the product. FIG. 4 is a chromatogram characteristic ofrelatively “low odor” extruded pellets substantially free of C8 and C9ketones as shown. Generally, “low odor” compositions reduceconcentration of C8 and C9 ketones over “high odor” compositions by⅔with ⅕being typical and {fraction (1/10)} being preferred. Thus, ingeneral, melt compounded compositions in accordance with the inventionhave extractable concentrations of C8 and C9 alkyl ketones of less thanabout 3.5 ppm (weight) with less than 2 ppm being typical and less than1 ppm being particularly preferred.

It can also be seen from the chromatograms in FIGS. 3 and 4 that theadjacent C7 ketone levels are comparable in both the “low odor” and“high odor” compositions. Thus, the C8/C7 ratio can be used as analternative indicator of desirable olfactory characteristics. Typically,“low odor” compositions in accordance with the invention have a C8/C7ratio at least five times less than high odor compositions with at leastten times less being typical.

In preferred compositions according to the invention, C8/C7 ratios asmeasured by Likens-Nickerson extraction followed by gaschomatography/mass spectrometry are generally less than about 0.5 or soas is seen from in the examples which follow. C8/C7 ratios of less thanabout 0.3 are typical and C8/C7 ratios of less than about 0.1 areparticularly preferred. The articles of the invention and the pelletsfrom which they are made are further characterized by a relative aromaintensity index which is determined by commercially available equipmentin accordance with the procedure detailed below.

Relative Aroma Intensity Index

Melt processed compositions produced in accordance with the presentinvention, particularly extruded pellets from which articles such asplates and bowls are made, characteristically exhibit relatively lowodor as opposed to conventionally formulated mica/polypropylenecompositions. Generally the relative aroma intensity index (as definedherein) is less than about 1.6, with less than or equal to about 1 beingpreferred. In general, the lower the relative aroma intensity index, thelower the odor intensity of the mica/polypropylene pellets. Less than orequal to about 0.7 is most preferred with a practical lower limitbelieved to be somewhere around 0.1 or so. Thus, in accordance with theinvention, melt compositions will generally have a relative aromaintensity index of less than about 1.6 and typically from about 1.5 toabout 0.1. Within the range of from about 1.0 to about 0.1 is moretypical, while a relative aroma intensity index of from about 0.7 toabout 0.1 is preferred.

The relative aroma intensity index (RAII) of a particular melt-processedcomposition is readily determined using conventional materials andequipment.

The relative aroma intensity index is defined as the arithmetic averageof all sensor integrals for a given sample divided by the arithmeticaverage of all sensor integrals for a standard sample specified below;or in equation form:${RAII} = \frac{{Arithmetic}\quad {Average}\quad {of}\quad {Odor}\quad {Intensity}\quad {over}\quad {all}\quad {sensors}\quad {of}\quad {sample}}{{Arithmetic}\quad {Average}\quad {of}\quad {Odor}\quad {Intensity}\quad {over}\quad {all}\quad {sensors}\quad {of}\quad {standard}\quad {composition}}$

A commercially available- aroma scanning device is used. Typically, suchdevices utilize a plurality of conductivity sensors to determine theodor of a sample. The particular device used in the discussion whichfollows uses 32 sensors whose response is integrated over time. Thevarious integrals are arithmetically averaged for each sample (orstandard composition as the case may be). This arithmetic average isthen used in both the numerator or the denominator in the above notedequation.

The standard composition utilized for determining RAII herein isproduced from the following components:

TABLE 7 Standard Composition Amount (Wt. Component Manufacturer ProductNumber Percent) Polypropylene Exxon Escorene 4772 55.63 Mica FranklinL-140 30.0 Industrial Minerals, Inc. Calcium Huber Q-325 10.0 CarbonateCoupling Agent Aristech Unite NP-620 2.5 Titanium Tioxide TR-23 1.87Dioxide

The above components were extruded on a 90 mm Berstorff Co-Rotating TwinScrew Extruder with underwater pelletizing under the followingconditions:

200 rpm screw speed

with the following set temperature profile:

Zone 1—510° F.

Zone 2—485° F.

Zone 3—400° F.

Zone 4—380° F.

Zone 5—380° F.

Zone 6—380° F.

Head Flange -425° F.

Screen Changer-425° F.

Die-440° F.

Throughput appx. 900 LB/HR to produce the standard pellets. By theforegoing definition, these standard pellets have a relative aromaintensity index (RAII) of 1.0.

The preferred instrument to perform the aroma intensity measurements isan Aroma Scan® model A32 (AromaScan, Hollis, N.H., USA). This instrumentemploys a dynamic head space type of measurement, in which nitrogen gasflows through a sample vial and carries aroma volatiles to the sensors.All pellet samples are analyzed in triplicate with the final resultsaveraged to minimize measurement noise. In the illustrations whichfollow, The “Acquisition Parameters” method of the instrument is setwith a sampling interval of 1 and a detection threshold of 0.2. The“Multisampler-SP” method of the instrument sets the platen temperature(100° C. for the examples herein). Two other temperatures (115° C. and125° C.) are automatically set. The Multisampler-SP method is also usedto set the parameters in Table 8 to measure aroma intensity.

TABLE 8 AromaScan ® Settings Sample Equilibration Time 5 minutes VialSize 22 ml Mix Time  0 Mix Power  1 Relative Humidity 10% Sampling Time4 minutes Wash Time 5 minutes Data Collection Time 19 (minutes) TimeBetween Injections 20 (minutes)

In the recognition window, start and end are set at 1. In addition tothe foregoing, the “Vial Pressurization Control” is set at 20 kPa, the“Vial Needle Flow” is set at 50 ml/min nitrogen; “Transfer Line Flow”across the sensors, between, before and after samples is set at 150m/min. All gas flows are for dry nitrogen.

A response of each of the 32 sensors of the AromaScan® machine isintegrated over a time interval of 55-150 seconds. The initial 55seconds is allowed to let humidity/moisture exit the system to a greatextent before integration is started. The 150 second integration endtime was chosen to allow the sensor signals to return to baseline, atwhich time all significant signal has been integrated. The varioussignals seen after 150 seconds are insignificant in terms of the odormeasurement, as can be seen from FIG. 5. FIG. 5 is a plot of sensorresponse vs. time for each of the 32 sensors of the Aroma Scan device,where individual responses are shown as various lines on the diagram.

Using the foregoing procedure, 2.0 grams of compounded polymer pelletsare weighed and placed in the 22 ml, crimp top, septum capped vials andanalyzed automatically by the instrument. There is shown in FIG. 6 theresults for various extruded polypropylene/mica pellets. The data pointsshown on FIG. 6 are actually the response integrals for a particularsensor.

The abscissa on FIG. 6 indicates each of the 32 elements; while theordinate is the time-integrated response of the corresponding element inarbitrary units. There is shown as curve A the (integrated) sensorresponses for the standard sample prepared as above. As noted before,this sample has a relative aroma intensity index of 1.0 by definition.There is also shown a sample prepared in accordance with the standardsample procedure except that polypropylene was substituted for calciumcarbonate at curve B as in the “high odor” compositions of the KansasState Trials discussed above in connection with Examples 12-17. As canbe seen, this composition has a relative aroma intensity index of about1.6; or in other words, its response integrals are on average 1.6 timesthose of the standard sample. There is also shown on FIG. 6 a thirdcurve (C) representative of more preferred compositions prepared inaccordance with the present invention. Curve C represents a compositionprepared in accordance with Examples 28 through 30 below (Table 11)wherein the relative aroma intensity index is less than about 0.7 whichmeans its response integrals are on average less than 0.7 times those ofthe standard sample.

Through the use of an automated instrument, the aroma intensity of themelt-compounded pelletized composition can be reduced to a single value.While the foregoing sets forth a particular and preferred method ofdetermining the relative aroma intensity index, it may also be possibleto employ other instruments consistent with this protocol since suchinstruments are readily available. If such alternative instrument isemployed the standard composition detailed above should be used toensure that calibration is proper. As noted, the standard compositionhas a RAII of 1.0 while a composition prepared substitutingpolypropylene for the calcium carbonate of the standard composition hasa RAII of about 1.6 or above and a composition prepared in accordancewith Examples 28 through 30 should have a RAII of 0.7 or less. By usingthese multiple reference points, the relative aroma intensity index isalways readily determined by one of skill in the art.

EXAMPLES 18-26

A series of resin compositions and sheet products were prepared inaccordance with the discussion above and characterized by C8/C7 ketoneratio and odor panel testing. Variables included calcium carbonateaddition, process atmosphere (air or nitrogen) and process melttemperature. Results appear in Table 9 for examples 18 through 26.

TABLE 9 CaCO₃ Effect of Process Conditions and Compositions on Odor ofPP/Mica Composites Process Odor Panel Data Type (Banbury or AtmosphereCaCO₃ Process Melt C₈/C₇ Sustained “Scorched” Odor Profile ExampleExtruded Sheet) (Air/N₂) (Yes/No) Temperature Ketone Ratio (TotalIntensity) Component Intensity 18 Brabender Banbury Air Yes 370° F.0.055 2.0 0 Compounded 19 Brabender Banbury Air Yes 460° F. 0.6 4.0 5.0Compounded 20 Sheet N₂ Yes 460° F. 0.3 21 Brabender Banbury Air Yes 460°F. 0.6 40 5.0 Compounded 22 Sheet Air Yes 370° F. 0.15 2.0 0 23 SheetAir No 370° F. 1.3 6.0 4.5 24 Sheet Air Yes 400° F. — 5.0 2.5 25 SheetAir No 460° F. 0.9 8.0 3.5 26 Sheet Air Yes 460° F. 0.7 2.0 0 Seediscussion above for C₈/C₇ ketone ratio, odor; Kansas State UniversityOdor Panel Profile. Extruded Sheet was prepared using a single screwextruder with pre-compounded resin made by a twin screw process.

The resins of Examples 18, 19, and 21 were prepared on a Brabenderdevice (C.W. Brabender, model EPL2V5502) with a Banbury mix head (modelR.E.E.6, 230v, 11a) with a mixing time of 5-10 minutes

The sheet samples, Examples 20 and 22 through 26, were prepared fromprecompounded resin pellets extruded under the conditions shown in Table10.

TABLE 10 Sheet Extrusion Conditions for PP/Mica Pilot ExtruderCONDITIONS ACTUAL SET POINT Barrel Zone 1 (° F.) 354-378 360-375 BarrelZone 2 (° F.) 366-410 370-410 Barrel Zone 3 (° F.) 371-460 370-460Adapter temp (° F.) 359-460 370-460 Feed Block Temp (° F.) 370-468370-460 Die Zones 1-3 temps (° F.) 368-462 370-460 Extruder RPM 110 110Drive Amperes 15-23 — Melt Pressure (psi) 1050-1850 — Die Pressure (psi)745-910 — Line Speed (FPM) 8.25-9.74 — Chill roll temp. (° F.) 130 —

The odor of PP/mica composites (pellets or sheet) is affected bytemperature, atmosphere, and by the addition of a basic filler such asCaCO₃. The C8/C7 ketone ratio is consistent with the odor panel data andshows that offensive odor components decrease with:

Using lower processing temperatures

Using a base such as CaCO₃ as a buffering agent

Processing under inert atmosphere such as N₂.

EXAMPLES 27-30

Particularly preferred, low odor compositions are prepared by way of asequential process in a Banbury mixer at relatively low temperatures. Atypical Banbury apparatus is shown schematically in FIG. 7. An apparatus110 includes generally a feed hopper 112 provided with a feed ram 114coupled to a weight cylinder 116 which may be varied depending on theforce required for a particular process. Feed hopper 112 has a lowerportion 118 which communicates with a mixing chamber 120 provided with apair of rotors 122, 124. The material is supplied to hopper 112 througha charging door indicated at 126, and/or fed through a feed port locatedat 128. Chamber 120 is further provided with a discharge door 130 whichis positioned above a conveyor indicated at 132. Such apparatus is wellknown for compounding thermoplastic compositions.

A conventional non-sequential process is operated as follows: (a)discharge door 130 is closed; (b) ram 114 is drawn up; (c) theingredients are added; (d) the ram is lowered and the rotors activated;(e) mixing is complete when a combination of temperature and work hasbeen achieved (power draw on mixer motor falls off); (f) at which pointthe discharge door is opened and the batch is gravimetrically suppliedto a conveyor; and finally (g) the batch is conveyed to a single screwextruder and pelletized. The apparatus melts the polymer through sheargenerated by the rotors and walls against the components being mixed.One may rely on shear (that is, mechanical work) to soften thethermoplastic components or apply some auxiliary heat directly either inthe feed hopper or the chamber through the use of heating coils,infrared devices, steam jacketing and the like, or, alternatively,preheating the polymer externally prior to feeding.

It has been found that melt compositions prepared in a sequentialBanbury process exhibit superior stiffness as measured by flexuralmodulus properties and low odor. In a sequential process in accordancewith the invention, two feed steps are used in order to minimize thetime heated or molten polypropylene is in contact with the mica as willbe explained in connection with FIGS. 7 and 8.

In a first, melt mix step, door 130 is closed and ram 114 is drawn up.Polypropylene, polyethylene, titanium dioxide, other pigments and thelike are added. Ram 114 is lowered and the rotors 122, 124 are rotatedto shear the material. A typical power curve (at constant rotor speed)for amperage supplied to the mixing motors for the inventive sequentialprocess is shown in FIG. 8, a plot of amperage versus time inhours:minutes:seconds.

When the pair of rotating rotors are first started in the melt mix step,the current draw is indicated at point P1 on FIG. 8 where it can be seenpower applied to the polymer is quite high. The current draw reaches amaximum at about P2 where the polymer begins to soften rapidly. At P3after a minute or two the current draw is at a minimum while thecomponents are being mixed when the polymer is in a softened state. Micaand calcium carbonate may then be added simultaneously in a micaaddition step as will be detailed below.

After the polymer is softened, ram 114 is again drawn up and the micaand calcium carbonate may be added at the time corresponding to P4 onthe diagram. The material may be added through a door 126 or feed port128. The current draw at constant rotor speed again increases as shownat P5 and eventually begins to decay as shown at P6 and P7. Morepreferred is to add the mica and calcium carbonate mixture at about thetime corresponding to P2 prior to complete softening of the resin.Alternatively, polypropylene may be externally preheated to about 240°F. or so (along with the mixing chamber to the same temperature) and allof the ingredients are simultaneously added for maximizing processthroughput. Preferred drop batch temperature at the end of Banbury meltcompounding, that is, maximum melt processing temperature for this stepis up to about 425 degrees Fahrenheit. At the time corresponding to P7,the door may be opened and the batch of material (a batch size is about200 pounds) conveyed to an extruder to be pelletized.

TABLE 11 Comparison of Compounding Processes Compound Flexural ModulusRelative Aroma COMPOUNDING (Tangent), 9″, Plate Intensity Index PROCESSPSI Rigidity (g/0.5″) (Compound) Twin Screw 718,000 417 1.0 Example 27Banbury 591,000 378 0.59 (non- sequential) Example 28 Banbury 708,000416 0.65 (sequential, 1 min. pre-heat) Example 29 Banbury 635,000 3520.62 (Sequential, 2 min. premelt) Example 30

Table 11 shows compound flexural modulus (as measured by ASTM method D790-95a), corresponding plate rigidity, and aroma intensity index onfour indicated compounding processes designated as examples 27-30. Inthe case of twin-screw (Example 27), high modulus is obtained but withhigher odor with relatively low throughput, in the range of 900 lb/hr,which is less than half the output of Banbury compounding processes(utilizing a Stewart-Bolling Banbury Mixer with batch sized in the rangeof 150-200 lb) listed herein. In the case of non-sequential Banburyprocess, low modulus is obtained with corresponding low plate rigiditywith lower odor and high throughput. In the last two cases correspondingto sequential Banbury processes designated as “1 min. pre-heat” and “2min. pre-melt”, the short 1 minute preheat case (Example 29) ispreferred because it gives high compound modulus and high plate rigidity(comparable to twin screw case) with benefits of both low odor and highthroughput, in excess of 2000 lb/hr.

The twin screw formulation in the above table contains PP/30% mica/10%CaCO3 with 2.5% coupling agent (maleic anhydride modified PP gradeAristech Unite NP-620) and no polyethylene. The formulationcorresponding to all three listed Banbury processes in above tablecontain PP/30% mica/10% CaCO3/0.5% Ti02/4%LLDPE with no coupling agentwhere such ingredients have the following sources and grades:Mica=Franklin Minerals L-140, CaCO₃=Huber Q325, PP=Exxon EscorenePP4772, LLDPE=Novapol Novachemical G1-2024A.

The Banbury “non-sequential” case (Example 28) in Table 11 correspondsto adding all ingredients together with a total compounding time ofabout 4.5 minutes followed by conversion of the batch (havingtemperature of 430° F.) to pellets using a continuous 10″single screwextruder equipped with one 30 mesh and one 20 mesh screen, and anunderwater pelletizing die assembly, with a pelletizing temperature inthe range of 455-470° F.

The Banbury “sequential 2 min premelt” case (Example 30) in Table 11corresponds to a 2 minute period for melting the PP/LLDPE mixture (inthe presence of CaCO₃ and TiO2) to a maximum temperature of about 350°F., followed by adding mica and thereafter mixing for a period of about105 sec to achieve a batch temperature of about 430° F., followed byconversion to pellets with a pelletizing temperature of about 460° F.The Banbury “sequential, 1 min pre-heat” case (Example 29) in Table 11corresponds to about a 1 minute period for presoftening the PP/PEmixture (in the presence of TiO2, or alternatively adding the TiO₂ withthe mica and calcium carbonate) to a maximum temperature of about 260°F., followed by adding the mica/CaCO₃ mixture and thereafter mixing toachieve a batch temperature of about 425° F., followed by conversion topellets with a pelletizing temperature of about 425° F. In thispreferred mode, it has been found that polymer preheating aids inpreserving compound stiffness (required for rigid articles ofmanufacture) and intimate contact of mica with odor suppressing agent(CaCO₃) aids the production of low odor material.

Pellets from the above mentioned Banbury compounding processes weresubsequently extruded at 370° F. as cast sheets in the range of 17-18mil. Sheet line conditions also included a screw RPM value of 100, achill roll temperature of about 130° F., drive amperage value of about22, melt pressure of about 2000 psi, die pressure of about 970 psi, anda line speed of about 7 ft/min. Plates were subsequently vacuumthermoformed using a female mold and trimmed and tested for rigidity.

EXAMPLES 31-41

Extruded mica filled polypropylene sheets prepared as described inExamples 1 through 8 were characterized with respect to surface glossand roughness. Table 12 shows 75 degree gloss and Parker Roughness(airflow method) data for an extruded mica filled polypropylene sheetversus same properties for the food contact (air) side of vacuum formed10.25 inch plates produced according to condition (B) of FIG. 2 usingthe same sheet formulation. The unique thermally induced micronodularsurface is characterized by significant decrease in gloss andsignificant increase in roughness as shown in the two photomicrographsin FIGS. 9A and 9B, which results in a stoneware or pottery likeappearance with aesthetic appeal. (The Parker Roughness method isdescribed above). The upper photomicrograph of FIG. 9A is of athermoformed plate surface, while the lower photomicrograph of FIG. 9Bis of sheet.

The photomicrographs of FIGS. 9A and 9B were obtained from a 10×15 mmpiece cut out of a plate bottom. The sheet sample was mounted withsurface of interest up on a specimen stub, and coated withgold/palladium. The stub was placed in a JEOL 840A Scanning ElectronMicroscope (SEM). Photomicrographs of the samples were taken at75×magnification, 30 degree tilt, 39 mm working distance at 3 kv.

TABLE 12 GLOSS AND ROUGHNESS PROPERTIES OF THE FOOD CONTACT SIDE OFPOLYPROPYLENE/MICA/TIO₂ PLATE SURFACE VERSUS NEAT EXTRUDED SHEET GLOSSPARKER ROUGHNESS EXAMPLE (75 DEGREES) * (MICRONS) 31 (Plate) 22.4 13.4132 (Plate) 30.6 14.05 33 (Plate) 24.8 14.89 34 (Plate) 24.3 14.24 35(Plate) 24.5 12.48 PLATE AVERAGE 25.3 ± 3.1 13.8 ± 0.9  36 (Sheet) 45.75.92 37 (Sheet) 47.2 7.43 38 (Sheet) — 5.89 39 (Sheet) — 6.35 40 (Sheet)— 5.84 41 (Sheet) — 8.15 SHEET AVERAGE 46.5  6.6 ± 0.97 * = Average ofMachine and Cross Machine Directions

As shown in Table 12, the food contact side is rougher as evidenced byincreased roughness and decreased gloss relative to the neat extrudedsheet. The rough appearance is desirable for purpose of creating themicronodular surface giving the container and plate a stoneware orpottery-like look.

EXAMPLES 42-43

Mica filled polypropylene sheets were successfully vacuum thermoformedinto 12 oz. oval microwave containers, whereby the base was producedusing mode (B) of FIG. 2 and the lid was produced using mode (A) of FIG.2. In contrast, attempts to form unfilled polypropylene sheet into thesame container were not successful.

EXAMPLES 44-46

Sheet rolls ( 17.5 wide), at three calipers were extruded as describedin Examples 1 through 8 in connection with FIG. 1. Table 13 summarizesthe PP/40% mica material and process conditions. Table 14 summarizes thePP/40% mica sheet properties.

TABLE 13 PP/Mica Extrusion Process Conditions Summary Barrel BarrelBarrel Feed Zone 1 Zone 2 Zone 3 Adaptor Block Line Die Zone 1 PlateSize Temp. (F.) Temp. (F.) Temp. (F.) Temp. (F.) Temp. Speed Temp. (F.)(in.) Actual/Set Actual/Set Actual/Set Actual/Set Actual/Set (fpm)Actual/Set 11 395/395 452/425 475/475 470/470 470/470 9.27 470/470 10376/375 410/410 431/430 430/430 430/430 8.32 430/430 9 375/376 410/410434/430 430/430 430/430 8.07 430/430 Die Zone 2 Die Zone 3 Screw MeltDie Chill Roll Plate Size Temp. (F.) Temp. (F.) RPM Drive PressurePressure Temp. (F.) (in.) Actual/Set Actual/Set Actual/Set Amperes (psi)(psi) Actual/Set 11 469/470 470/470 125 18.3 1387 694 130/130 10 430/430430/430 130 19.3 2012 737 130/130 9 430/430 430/430 132 24.2 2112 686130/130

TABLE 14 PP/Mica Sheet Property Summary Plate Size Overall BasisWeight-Avg. (in.) Overall Caliper-Avg. (mil) (lb./3000 ft.{circumflexover ( )}2) 11 18.46 ± 0.36 308.07 ± 13.72 10 17.20 ± 0.10 288.80 ±9.89  9 16.94 ± 0.10 268.11 ± 7.50 

Example 47-49

Plates from sheet specifications set forth in Examples 31-41 wereproduced using 1-up water cooled female molds ( with pressure box/vacuumassembly), followed by matched metal punch trimming. Mold temperaturewas 70° F., while sheet temperatures for the 9, 10, and 11 inch plateruns were respectively 300° F., 310° F., and 295° F. The 9 and 10 inchplates were produced at 20 cycles/minute while the. bulk of the 11 inchplates were made at 25 cycles/minute.

Oven temperature control on the commercial machine was good due to thecombination of top quartz heaters and bottom calrod heaters with properzoning. In general, higher temperatures produce more micronodularity atthe expense of more pronounced sheet sag and wrinkling while lowtemperatures tend to reduce sag at the expense of diminished stonewareor pottery-like appearance.

Best results (i.e., micronodular matte eating surface without “webbing”or wrinkling) were obtained by increasing the top oven temperature by3-5° F. and decreasing the bottom by a corresponding amount. Thisability to selectively control oven temperature in effect facilitateddetermination of the preferred process temperature window of PP/micasheets.

EXAMPLES 50-54

Sheets and plates were prepared as illustrated in Examples 1 through 8and FIGS. 1 and 2. Table 15 shows sheet extrusion and formingconditions. FIGS. 10 and 11 respectively, show gloss and plate rigidityversus mica level (at constant mica/TiO₂ ratio).

TABLE 15 Extrusion/Forming Conditions Barrel Zone 1 375° F. Barrel Zone2 410° F. Barrel Zone 3 430° F. Adaptor 430° F. Feedblock 430° F. DieZones 1/2/3 430° F. RPM 130 Chill Roll 130° F. Target Sheet Caliper 18.3mil Sheet Width 18.0 inches Comet Former Top Heater 20% Comet FormerBottom Heater 35% Comet Former Time 50-60 seconds Plate Diameter   11inch

EXAMPLES 55-62

Commercial sheet extrusion runs of several mica filled polypropyleneformulations were conducted. These sheets suitably have a basis weightof about 200 to 950, per 3000 square foot ream, preferably about 200 to400 per 3000 square foot ream. These mica filled polypropylene sheetshad a mica content in the range of 25 to 35 weight percent.

The extrusion of coupled mica and polypropylene blends was conducted ona 6″ commercial extruder line. The extruder was an Egan 24/1 L/D with ageneral purpose screw. The die was an Extrusion Die Inc. 52″ coat hangertype. The stack conditioning rolls were top polished chrome, middlematte (40 RA surface), and bottom polished chrome. The matte chill rollassisted with the formation of the micronodular surface duringthermoforming of the sheet with beneficially improving breadth offorming temperature window in contrast with non-matted smooth sheets.The differences between surfaces of the various sheets and plates madetherefrom may be better appreciated by reference to FIGS. 12 and 13hereof. FIG. 12A is a scanning electron photomicrograph of surface A ofTable 16, while FIG. 12B is a scanning electron photomicrograph ofsurface B of Table 16. FIG. 13A is a scanning electron photomicrographof surface G of Table 16 and FIG. 13B is a scanning electronphotomicrograph of surface H of Table 16.

The roughness of various surfaces is compared in Table 16 below.

TABLE 16 Roughness and Gloss Properties of PP/30% Mica Extruded Sheetsand Thermoformed Plates Sheet Thermoforming Temperature Parker RoughnessSurface (° F.) (microns) Gloss (75%) A —  8.56 ± 0.39  4.99 ± 0.11 B —15.82 ± 0.74  8.05 ± 0.30 C 305 13.14 ± 0.74 14.3 ± 1.0 D 300 11.74 ±0.86 11.6 ± 1.0 E 292 12.10 ± 0.82 11.7 ± 1.0 F 265 10.63 ± 0.68 8.20 ±0.6 G — 6.17 82.10 H — 5.14 80.75 (A) Matte extruded sheet having topmatte side. (B) Extruded sheet (A) - bottom side opposite to matte side(C, D, E, F) Plate - eating side corresponding to top matte side of (A)(G) Non-matte extruded sheet - top side (no matte roll) (H) Non-matteextruded sheet - bottom side (no matte roll)

For a non-matte extruded sheet, usually plate gloss and plate roughnessare inversely related (e.g., high gloss corresponds to low roughness andvice versa as demonstrated in prior art data generally obtained). Inthat case, achieving desirable micronodular texture is within atemperature range (about 295° F. to 305° F.) where above this range theforming process is sag limited while below this range the plate exhibitspoor micronodular character as manifested by high gloss and lowroughness.

The use of a matte roll in the chill roll stack portion of the extrusionprocess effectively broadens the commercially attractive thermoformingprocess temperature range (about 265° F. to 305° F.). Specifically,plates having acceptable surface micronodularity can be formed at lowertemperatures, whereby the decrease in plate roughness is compensated byan unexpected decrease in plate gloss using sheet surface (A). Thisbeneficial increase in plate forming temperature window from about 10°F. to about 40° F. is brought about by imparting a matte surface finishto the extruded sheet.

The extruded sheet used in the suitable forming and thermoformingprocess, or the preferred thermoforming process as shown in FIG. 2 has athickness of about 0.010 to 0.080 inches, suitably 0.010 to 0.030inches, and preferably 0.015 to 0.25 inches. Suitable mica fillerloading level in the extruded sheet is in the range of 25-30 weightpercent, whereby mica flake aspect ratio is in the range of 30-300, morepreferably 80-120, with particle size range of about 50-500 microns.

By matte finishing one side of the sheet using matte roll, thecommercial thermoforming was suitably conducted at a broader temperaturewindow of about 265° F. to 305° F. while without matte finishing, thethermoforming using the same commercial equipment was conducted at atemperature of about 295° F. to 305° F.

The runs on commercial equipment using PP/30% mica and PP/25% micaformulations showed that the thermoforming temperature window range hasbeen expanded from about 10° F. (previous trial) to as high as about 35°F. This is primarily due to the fact that we beneficially used a matteroll in the chill roll stack during the extrusion process. This gave asmooth matte finish for the air side of the sheet (i.e., plate eatingsurface) while the rougher bottom side was in contact with thesandblasted mold side during the forming process. Use of matte sheet, inturn, enabled-forming at lower temperatures (which is good for sagavoidance) without much loss in micronodularity. Specifically, theforming window was in the range of 265° F. to about 300° F. to 305° F.where best balance of process stability and product appearance/texturewas seen at about 280° F. to 290° F.

Preferred Articles

The sheet of the present invention is suitably formed into plates orbowls having a circular configuration. These articles of manufacture mayalso be square or rectangular in shape having angular corners, such asfound in a tray. Further, additional shapes such as triangular,multi-sided, polyhexal, etc., are contemplated including compartmentedtrays and plates as well as oval platters. In each contemplatedembodiment, all corners are rounded or curved with a preferred pluralityof embodiments of the present invention being depicted in FIGS. 14through 33. The various embodiments shown in FIGS. 14 through 33, whileillustrative of the present invention, are not intended to limit theinvention and those of skill in the art may make changes withoutchanging the essential characteristics of the invention. Thesecontainers may also have other features such as ridges, emboss, anddeboss patterns suitable for enhancing the properties of the containersof this invention. These container's bottom sections may have a convexcrown to improve stability and reduce rocking during use.

Throughout the following description, each of the dimensions arereferenced with respect to a given diameter D which, in accordance withthe present invention as illustrated in FIGS. 14 through 17 isapproximately 8.75 inches. However, the particular diameter of thecontainer is not a critical limitation and is only set forth herein byway of example. It is the relationship between the various portions ofthe rim configuration which are essential.

The planar inner region in accordance with the illustrated embodiment ofa plate in FIGS. 14 through 17 has a radius X1 which is equal toapproximately 0.3 D-0.4 D and preferably 0.348 D. This plate is descibedgenerally in U.S. Pat. No. 5,326,020 the disclosure of which isincorporated herein by reference. Adjoining an outer periphery of theplanar inner region 150 is a sidewall portion 152 including annularregion 154 having a radius of curvature equal to approximately 0.05D-0.06 D and preferably 0.0572 D with the center point thereof beingpositioned a distance Y1 from the planar inner region 150. Includedangle 156 of the annular region 154 is from about 40° to about 70° andpreferably about 60°-65° or approximately 62. Adjoining the periphery ofthe annular region 154 is the first frusto-conical region 158 whichslopes upwardly at an angle A1 with respect to the vertical from about20° to about 35° and preferably about 25°-30° or approximately 27.50°.Additionally, the frusto-conical region 158 is adjacent to the arcuateannular region 160 which includes a radius of curvature in the range of0.015 D to 0.03 D and preferably approximately 0.024 D with the centerpoint thereof being positioned a distance Y2 from the planar innerregion 150. The included angle 162 of the arcuate annular region 160 mayrange from about 61° to about 82° and is preferably 66° to 77° or about73°. The second portion 164 of the-arcuate annular region 160, that isthe distal portion of the arcuate annular region 160, is positioned suchthat a line tangent to the curvature of the arcuate annular region 160at the second portion 164 slopes downwardly and outwardly at an angle ofapproximately 0° to 12°.

The combination of the annular region 154 and arcuate annular region 160should combine to position the second portion 164 of the arcuate annularregion 160 in the manner set forth herein above. That is, the includedangle 156 of the annular region 154 when combined with the includedangle 162 of the arcuate annular region 160 with the firstfrusto-conical region 158 spanning therebetween, positions the secondportion 164 of the arcuate annular region 160 in a manner such that asecond frusto-conical region 166, which extends substantiallytangentially from the distal end of the second portion 164 of thearcuate annular region 160 extends outwardly and downwardly at an angleof about 0° to 12°. The second frustro-conical region 166 is of a lengthin a range from about 0.03 D to about 0.05 D and is preferably 0.04 D.Because the second frusto-conical region 166 extends substantiallytangentially from the second portion 164 of the arcuate annular region160, the second frusto-conical region 166 extends outwardly anddownwardly at an angle A3 in the range from approximately 0° to 12° withrespect to a horizontal plane formed by the planar inner region 150.

Adjoining an outer periphery of the second frusto-conical region 166 isthe lip 168 which is in the form of yet another frusto-conical regionwhich extends outwardly and downwardly from the second frusto-conicalregion 166. The lip 168 is of a length of at least 0.005 D and ispreferably approximately 0.010 D. Further, the lip (168) extends at anangle A2 of no more than 45° from vertical, preferably approximately 15°to 30° with respect to the vertical plane.

At the transition between the second frusto-conical region 166 and thelip 168 is a transition region 170. The transition region 170 includes aradius of curvature R3 which is in the range of about 0.008 D and 0.01 Dand is preferably approximately 0.0092 D with the center point thereofbeing positioned a distance Y3 from the planar inner region 150.Additionally, the transition region 170 has an included angle A4 ofapproximately 48° to 70°.

The plates disclosed in FIGS. 18 through 20 generally have thedimensions of the plates disclosed in U.S. Pat. No. 5,088,640 which isincorporated herein by reference in its entirety. These containers mayhave other features such as ridges, emboss, and deboss patterns suitablefor enhancing the properties of the containers of this invention. Thereis shown in FIGS. 18 through 20 a plate having a planar center includingan outer peripheral surface. The planar center forms a bottom for theplate. An outwardly projecting sidewall includes a first rim portionjoined to the outer peripheral surface of the planar center and a secondrim portion joined to the first rim portion. The first and second rimportions form a sidewall of the plate. A third rim portion is joined tothe second rim portion of the outwardly projecting sidewall and a fourthrim portion is provided for forming an outer edge of the container. Thefirst rim portion is joined to the peripheral surface of the planarcenter at an angle having a second predetermined radius. The third rimportion is joined to the second rim portion at an angle having a thirdpredetermined radius. The fourth rim portion is joined to the third rimportion at an angle having a fourth predetermined radius. The four radiias well as the four included angles are selected for enhancing rigidityof the plate as compared to a container made from the same material byother means as is further described below.

Illustrated in FIGS. 18-20, there is a plate 180 which includes a planarcenter 182 which, in turn, includes an outer peripheral surface 184.This center region 182 may have a slight convex crown to improve platestability during use. The planar center 182 forms a bottom for the plate180. An outwardly projecting sidewall 186 includes a first rim portion188 which is joined to the outer peripheral surface 184 of the planarcenter 182. A second rim portion 190 is joined to the first rim portion188. The first rim portion 188 and the second rim portion 190 form theoutwardly projecting sidewall 186 which forms the sidewall of the plate180. A rim 192 includes a third rim portion 194 which is joined to thesecond rim portion 190 of the outwardly projecting sidewall 186. Afourth rim portion 196 is joined to the third rim portion 194. Thefourth rim portion 196 forms the outer edge of the plate 180.

FIG. 20 illustrates a partial cross-sectional view of a plate, diameterD, according to the present invention. The plate 180 defines a centerline 204. A base or bottom-forming portion 200 extends from the centerline 204 to an outer peripheral surface 202.

From the center line 204 a predetermined distance X12 extends toward theouter peripheral surface forming portion 202. A distance Y12 extends apredetermined distance from the base or bottom-forming portion 200upwardly therefrom. A radius R12 extends from the intersection point ofthe distance X12 and Y12 to form a first rim portion 206 of theoutwardly projecting sidewall 205. The first rim portion 206 is definedby an arc A12 which extends from the vertical line defined at the outerperipheral surface 202 to a fixed point 210. The arc A12 may beapproximately 60°.

A distance X22 extends from the center line 204 to a predeterminedpoint. A distance Y22 extends from the base or bottom-forming portion200 of the plate 180 downwardly a predetermined distance. A radius R22extends from the intersection of the lines X22 and Y22 to form a secondrim portion 208 of the sidewall 205. The radius R2 extends from thefirst fixed point 210 to the second fixed point 212 through an arc A22.The arc A22 may be approximately 4°.

A distance X32 extends from the center line 204 to a predetermineddistance. A distance Y32 extends from the base or bottom-forming section200 of the plate 180 to project upwardly a predetermined distance. Aradius R32 extends from the intersection of the lines X32 and Y32 toform the third rim portion 214 of the rim 216. The radius R32 extendsfrom the second fixed point 212 to a third fixed point 218. An arc A32is formed between the second fixed point 212 and the third fixed point218 to extend a predetermined distance. The arc A32 may be approximately55°.

A distance X42 extends a predetermined distance from the center line204. Similarly, a distance Y42 extends from the base or bottom-formingsection 200 of the plate 180 to project outwardly. A radius R42 extendsfrom the intersection of the lines X42 and Y42 to form a fourth rimportion 217 of the rim 216. An arc A42 is formed between the third fixedpoint 218 and a fourth fixed point 220 at diameter D from the centerline. The arc A42 may be approximately 60°. A section 220 forms theouter edge of the plate.

The container made according to the present invention may have anyparticular size as desired by the user so long as the relative profiledimensions are maintained. More specifically, ovals, rectangles withrounded corners and other shapes may be made having this profile. Invarious embodiments of the present invention the container may be a9-inch or 11-inch plate with profile coordinates as illustrated in FIGS.18 through 20 having the dimensions, angles, or relative dimensionsenumerated in Tables 17 through 19.

TABLE 17 Dimensions and Angles For 9″ Plate DIMENSION and ANGLES VALUE(inches or degrees) R12 0.537 X12 3.156 Y12 0.537 R22 2.057 X22 5.402Y22 0.760 R32 0.564 X32 4.167 Y32 0.079 R42 0.385 X42 4.167 Y42 0.258A12 60.00° A22 4.19° A32 55.81° A42 60.00° D 9.00 BOTTOM CONVEX CROWN0.06

TABLE 18 Dimensions and Angles For 11′ PLATE DIMENSION/ANGLES VALUE(inches or degrees) R12 0.656 X12 3.857 Y12 0.656 R22 2.514 X22 6.602Y22 0.929 R32 0.689 X32 5.093 Y32 0.097 R42 0.470 X42 5.093 Y42 0.315A12 60.00° A22 4.19° A32 55.81° A42 60.00° D 11.00 BOTTOM CONVEX CROWN0.06

TABLE 19 Dimensions For 9 and 11 INCH PLATE DIMENSION RATIO VALUES(Dimensionless or degrees) OR ANGLE PREFERRED MINIMUM MAXIMUM R12/D0.060 0.045 0.075 X12/D 0.351 0.280 0.420 Y12/D 0.060 0.045 0.075 R22/D0.228 0.180 0.275 X22/D 0.600 0.480 0.720 Y22/D 0.084 0.065 0.100 R32/D0.063 0.050 0.075 X32/D 0.463 0.370 0.555 Y32/D 0.009 0.007 0.011 R42/D0.043 0.034 0.052 X42/D 0.463 0.370 0.555 Y42/D 0.029 0.023 0.035 A1260.00° 55.00° 75.00° A22 4.19° 1.00° 10.00° A32 55.81° 45.00° 75.00° A4260.00° 45.00° 75.00°

Salient features of the plate illustrated in FIGS. 18 through 20generally include a substantially planar center portion (which may becrowned as noted above and illustrated throughout the various figures)with four adjacent rim portions extending outwardly therefrom, each rimportion defining a radius of curvature as set forth above and furthernoted below. The first rim portion extends outwardly from the planarcenter portion and is convex upwardly as shown. There is defined by theplate a first arc A12 with a first radius of curvature R12 wherein thearc has a length S1. A second rim portion is joined to the first rimportion and is downwardly convex, subtending a second arc A22, with aradius of curvature R22 and a length S2. A third, downwardly convex, rimportion is joined to the second rim portion and subtends an arc A32.There is defined a third radius of curvature R32 and a third arc lengthS3. A tangent to the third arc at the upper portion thereof issubstantially parallel to the planer center portion as shown in FIG. 20.A fourth rim portion is joined to the third rim portion, which is alsodownwardly convex. The fourth rim portion subtends a fourth arc A42 witha length S4, with a radius of curvature R42.

The length of the second arc, S2 is generally less the length of thefourth arc S4, which, in turn; is less than the length S1 of the firstarc A12. The radius of curvature R42 of the fourth arc is less than theradius of curvature R32 of the third rim portion, which in turn, is lessthan radius of curvature R22 of the second rim portion. The angle of thefirst arc, A12 is generally greater that about 55 degrees, while, theangle of the third arc, A32 is generally greater than about 45 degreesas is set forth in the foregoing tables. The angle of the fourth arc A42is generally less than about 75 degrees and more preferably is about 60degrees.

Typically, the length S1 of arc A12 is equivalent to the length S3 ofarc A32 and R12 of the first rim portion is equivalent in length to theradius of curvature R32 of the third rim portion.

Generally speaking, the height of the center of curvature of the firstarc (that is the origin of ray R12) above the central planar portion issubstantially less than, perhaps twenty five percent or so less than,the distance that the center of curvature of the second rim portion (theorigin of ray R22) is below the central planar portion. In other words,the length Y12 is about 0.75 times or less the length Y22.

So also, the horizontal displacement of the center of curvature of thesecond rim portion from the center of curvature of the first rim portionis at least about twice the length of the first radius of curvature R12.The height of the center of curvature of the third rim portion above thecentral planar portion is generally less than the height of the centerof curvature of the fourth rim portion above the plane of the centralplanar portion. The horizontal displacement of the center of curvatureof the second rim portion is generally outwardly disposed from thecenter of curvature of the third and fourth rim portions.

A final noteworthy feature of the plate of FIGS. 18 through 20 is thatthe height of the center of curvature of the third rim portion above theplanar central portion is less than about 0.75 times the radius ofcurvature R42 of the fourth rim portion; while the height of the centerof curvature of the fourth rim portion above the plane of the centralportion is at least about 0.4 times the first radius of curvature R12.

Yet other embodiments of this invention include trays which have eitherthe DIXIE® Superstrong profile as illustrated in FIGS. 21 through 24and/or described in U.S. Pat. No. 5,326,020 assigned to the assignee ofthe present invention and incorporated herein by reference into thisapplication. These trays may have other features such as ridges, emboss,and deboss patterns suitable for enhancing the properties of the traysof this invention. Throughout the following description of FIGS. 21through 24, each of the dimensions are referenced to either the lengthD1 or the width D2, which are approximately 10.90 and 8.00 inchesrespectively. D1 is larger than or equal to D2. However, the particularlength and width of these containers is not a critical limitation and isonly set forth herein by way of example. It is the relationship betweenthe various portions of the rim configurations which are essential. Theplanar inner region 101 in accordance with the illustrated embodiment inFIGS. 21A through 24, has a length 1X which is equal to approximately0.3 D1 to 0.4 D1 and 0.3 D2 to 0.4 D2 and preferably 0.354 D1 andpreferably 0.342 D2. Adjoining an outer periphery of the planar innerregion 230 is a sidewall portion 232 including annular region 234 havinga radius of curvature equal to approximately 0.02 D1 to 0.03 D1 and0.025 D2 to 0.035D2 and preferably 0.023 D1 and 0.031 D2 with the centerpoint thereof being positioned a distance Y1 from the planar innerregion 230. Included angle 236 of the annular region 234 is from about40° to about 80° and preferably about 65° to 75° or approximately 69°.Adjoining the periphery of the annular region 234 is the firstfrusto-conical region 238 which slopes upwardly at an angle A1 withrespect to the vertical from about 10° to about 50° and preferably about15° to 25° or approximately 21°. Additionally, the frusto-conical region238 is of a length greater than about 0.05 D1 and 0.055 D2, preferablyfrom about 0.1 D1 to 0.2 D1 and 0.15 D2 to 0.25 D2 and more preferablyapproximately 0.15 D1 and 0.19 D2. Further, adjoining the firstfrusto-conical region 238 is the arcuate annular region 240 whichincludes a radius of curvature in the range of 0.005 D1 to 0.007 D1 and0.007 D2 to 0.009 D2 and preferably approximately 0.006 D1 and 0.008 D2with the center point thereof being positioned a distance Y2 from theplanar inner region 230. The included angle 242 of the arcuate annularregion 240 may range from about 40° to about 92° and is preferably 65°to 87. The second portion 244 of the arcuate annular region 240, that isthe distal portion of the arcuate annular region 240 is positioned suchthat a line tangent to the curvature of the arcuate annular region 240at the second portion 244 slopes downwardly and outwardly at an angle ofapproximately 0° to 12°.

The combination of the annular region 234 and arcuate annular region 240should combine to position the second portion 244 of the arcuate annularregion 240 in the manner set forth herein above. That is, the includedangle 246 of the annular region 234 when combined with the includedangle 242 of the arcuate annular region 240 with the firstfrusto-conical region 248 spanning therebetween, positions the secondportion 244 of the arcuate annular region 240 in a manner such that thesecond frusto-conical region 250, which extends substantiallytangentially from the distal end of the second portion 244 of thearcuate annular region 240 extends outwardly and downwardly at an angleof about 0° to 12°. The second frusto-conical region 250 is of a lengthin a range from about 0.045 D1 to about 0.055 D1 and 0.030 D2 to about0.040 D2 and is preferably 0.052 D1 and 0.034 D2. Because the secondfrusto-conical region 250 extends substantially tangentially from thesecond portion 244 of the arcuate annular region 240, the secondfrusto-conical 250 extends outwardly and downwardly at an angle A3 inthe range from approximately 0° to 12° with respect to a horizontalplane formed by the planar inner region 230.

Adjoining an outer periphery of the second frusto-conical region 238 isthe lip 252 which is in the form of yet another frusto-conical regionwhich extends outwardly and downwardly from the second frusto-conicalregion 250. The lip 252 is of a length of at least 0.006 D1 and 0.009 D2and is preferably approximately 0.010 D1 and 0.013 D2. Further, the lip252 extends at an angle A2 of no more than 45° from vertical, preferablyapproximately 10 to 30° with respect to the vertical plane and morepreferably approximately 20°.

At the transition between the second frusto-conical region 250 and thelip 252 is a transition region 254. The transition region 254 includes aradius of curvature R3 which is in the range of about 0.005 D1 to 0.007D1 and 0.007 D2 to 0.009 D2 and is preferably approximately 0.006 D1 and0.008 D2 with the center point thereof being positioned a distance Y3from the planar inner region 230. Additionally, the transition region254 has an included angle A4 of approximately 20 48° to 80 °.

There is shown in FIGS. 25 through 28 still yet another embodiment ofthe inventive articles. Throughout the following description of FIGS. 25through 28, each of the dimensions are referenced with respect to agiven diameter D which, in accordance with the present invention asillustrated in FIGS. 25 through 28, is approximately 7.5 inches.However, the particular diameter of the containers is not a criticallimitation and is only set forth herein by way of example. It is therelationship between the various portions of the rim configuration whichare essential. The planar inner region 260 in accordance with theillustrated embodiment in FIGS. 25 through 28, has a radius X1 which isequal to approximately 0.2 D to 0.3 D and preferably 0.25 D. Adjoiningan outer periphery of the planar inner region 260 is a sidewall portion262 including annular region 264 having a radius of curvature equal toapproximately 0.05 D to 0.15 D and preferably 0.11 D with the centerpoint thereof being positioned a distance Y1 from the planar innerregion 260. Included angle 266 of the annular region 264 is from about45° to about 75° and preferably about 60° to 70° or approximately 65°.Adjoining the periphery of the annular region 264 is the firstfrusto-conical region 268 which slopes upwardly at an angle A1 withrespect to the vertical from about 15° to about 45° and preferably about20° to 30° or approximately 25°. Additionally, the frusto-conical region268 is of a length greater than about 0.1 D preferably from about 0.17 Dto about 0.19 D and more preferably approximately 0.18 D. Further,adjoining the first frustro-conical is the arcuate annular region 270which includes a radius of curvature in the range of 0.015 D to 0.030 Dand preferably approximately 0.023 D with the center point thereof beingpositioned a distance Y2 from the planar inner region 260. The includedangle 272 of the arcuate annular region 270 may range from about 45° toabout 87° and is preferably 60° to 77°. The second portion 274 of thearcuate annular region 270, that is the distal portion of the arcuateannular region 270 is positioned such that a line tangent to thecurvature of the arcuate annular region 270 at the second portion 274slopes downwardly and outwardly at an angle of approximately 0° to 12°.

The combination of the annular region 264 and arcuate annular region 270should combine to position the second portion 274 of the arcuate annularregion 270 in the manner set forth herein above. That is, the includedangle 266 of the annular region 264 when combined with the includedangle 272 of the arcuate annular region 270 with the firstfrusto-conical region 268 spanning therebetween, positions the secondportion 274 of the arcuate annular region 270 in a manner such that thesecond frusto-conical region 276, which extends substantiallytangentially from the distal end of the second portion 274 of thearcuate annular region 270 extends outwardly and downwardly at an angleof about 0° to 12°. The second frusto-conical region 276 is of a lengthin a range from about 0.02 D to about 0.04 D and is preferably 0.03 D.Because the second frusto-conical region 276 extends substantiallytangentially from the second portion 274 of the arcuate annular region270, the second frusto-conical region 276 extends outwardly anddownwardly at an angle A3 in the range from approximately 0° to 12° withrespect to a horizontal plane formed by the planar inner region 260.

Adjoining an outer periphery of the second frusto-conical region 268 isthe lip 278 which is in the form of yet another frusto-conical regionwhich extends to outwardly and downwardly from the second frusto-conicalregion 276. The lip 278 is of a length of at least 0.01 D and ispreferably approximately 0.017 D. Further, the lip 278 extends at anangle A2 of no more than 45° from vertical, preferably approximately 10°to 30° with respect to the vertical plane and more preferablyapproximately 25°.

At the transition between the second frusto-conical region 276 and thelip 278 is a transition region 280. The transition region 280 includes aradius of curvature R3 which is in the range of about 0.007 D and 0.012D and is preferably approximately 0.009 D with the center point thereofbeing positioned a distance Y3 from the planar inner region 260.Additionally, the transition region 280 has an included angle A4 ofapproximately 48° to 80°.

There is shown in FIG. 29 yet another embodiment of a food contactarticle in accordance with the present invention. The containers of thisinvention may be formed as take-out containers, and a representativeembodiment, a suitable take-out container, will now be described ingeneral with respect to FIG. 29 wherein the lid and base may be formedas described in U.S. Pat. No. 5,377,860 which is incorporated herein byreference. While the container illustrated in FIG. 29 is oblong inconfiguration, the container may be round, oval, substantiallyrectangular or square as dictated by the contents which are to be placedwithin the container. The container 290 is formed of a base or bottomportion 292 and a lid 294. The lid 294 includes radially extendingopening tabs 296 which cooperate with the radially extending openingtabs 298 of the base 292 in order to allow the consumer to readily openthe sealed container. The base 292 of the container 290 includes asubstantially planar bottom 300 and a substantially vertically extendingperipheral sidewall 302. Integrally connected to the upstanding sidewall302 is a sealing brim 304 which is received within a cooperating sealingbrim 306 of the lid 294.

The lid 294 includes a substantially planar top portion 308 and a rim310 extending about a periphery of the top portion 398. The rim 310 isprovided in order to enhance the strength of an extended volume portion312 of the lid 294. The rim 310 also serves to locate the base 292 onthe lid when the lid is used as a stand.

The extended volume portion 312 is formed by extension wall 314positioned about the perimeter of the rim 310 and extending downwardlytherefrom. The extension wall 314 is integrally formed with a horizontallid reinforcing ring 316 which is substantially parallel to the topportion 308 of the lid 294. The outer perimeter of the lid reinforcingring 316 is further integrally formed with the sealing brim 306. Also,extending radially outward from the sealing brim 306 is a secondhorizontal lid reinforcing ring 318 which extends substantially parallelto the top portion 308 as well.

Similarly, the base 292 includes a horizontal lid reinforcing ring 320which extends from the periphery of the sealing brim 304 for aiding inand maintaining the structural integrity of the sealing brim 304 as wellas the container 290 as a whole. In addition to the reinforcing ring320, a step 322 may be provided about an upper portion of the peripheralsidewall 302 for preventing nested units from becoming jammed togetherdue to excessive interpenetration when stacked and nested. Also, formedin an upper portion of the sidewall 302 are undercuts 324 whichcooperate with detents 326, only one of which is illustrated in FIG. 29at the integral connection between a brim 306 and lid reinforcing ring316. The detents, when engaged in the undercuts 324, provide an audibleindication that the container is in fact sealed. Additionally, undercuts328 may be provided in an outer periphery of the brim 304 for receivingdetents 330 formed in an outer portion of the brim 306 for againproviding an audible indication that the container is sealed. While thecontainer illustrated in FIG. 29 shows detents and undercuts formed inboth the inner and outer portions of the brims 324 and 306,respectively, it may be desired to provide respective detents andundercuts on only one side of the brim or to provide no undercuts anddetents on either side of the brim.

In a yet still further embodiment of this invention another bowl isillustrated in FIGS. 30 through 33. Throughout the following descriptionof the bowl of FIGS. 30 through 33, each of the dimensions arereferenced with respect to a given diameter D which, in accordance withthe present invention as illustrated is approximately 7.3 inches.However, the particular diameter of the containers is not a criticallimitation and is only set forth herein by way of example. It is therelationship between the various portions of the rim configuration whichare essential. The crowned inner region 340 in accordance with theillustrated embodiment in FIGS. 30 through 33, has a crown height Y5which is approximately 0.004 D to 0.012 D or preferably 0.008 D, andencompassing a radius X1 which is equal to approximately 0.2 D to 0.3 Dand preferably 0.25 D. Adjoining an outer periphery of the crowned innerregion 340 is a sidewall portion 342 including first annular region 344having a radius of curvature equal of approximately 0.05 D to 0.15 D andpreferably 0.11 D with the center point thereof being positioned atdistance Y1 from the tangency point between the crowned inner region 340and the first annular region 344. Included angle 346 of the firstannular region 344 is from about 45° to about 85° and is preferably 65°to 80° or approximately 72°. Adjoining the periphery of the firstannular region 344 in the sidewall portion 342 is a second annularregion 348 having a radius of curvature equal of approximately 0.8 D to1.2 D and preferably 0.96 D with the centerpoint thereof beingpositioned a distance Y2 from the tangency point between the crownedinner region 340 and the first annular region 344. The included angle ofarc A2 indicated generally at 350 of the second annular region 348 isfrom about 2° to 12° and is preferably 5° to 9° or approximately 7°.Adjoining the periphery of the second annular region 348 in the sidewallportion 342 is a third annular region 352 having a radius of curvatureequal to approximately 0.1 D to 0.2 D and preferably 0.15 D with thecenterpoint thereof being positioned a distance Y3 from the tangencypoint between the crowned inner region 340 and the first annular region344. Included angle 354 of the third annular region 352 is from about20° to 50° and is preferably 25° to 40° or approximately 33°. Adjoiningthe sidewall portion 342 is a flange portion 356 including a fourthannular region consisting of regions 358 and 360 which have the sameradius of curvature. Adjoining the third annular region 352 is a fourthannular region beginning with annular region 358 which extends to theuppermost bowl height and continuing with annular region 360 to bowldiameter D. Annular regions 358 and 360 are equivalent to one annularregion, flange portion 356 since both have the same radius of curvatureof approximately 0.02 D to 0.05 D and preferably 0.03 D with thecenterpoint thereof being positioned a distance Y4 from the tangencypoint between the crowned inner region 340 and the first annular region344. Included angle 362 of the fourth annular region 356 is from about45° to 85° and preferably 65° to 80° or approximately 73°.

Physical Properties, Heat Resistance and Food Contact Suitability

FIG. 34 shows rigidity versus current plate material cost comparisonsfor mica filled polypropylene plates versus competitor plasticdisposable plates. “J” refers to mica filled polypropylene plate of thisinvention and “S” refers to polystyrene based plates such as thosecurrently manufactured by Solo Cup Company. Average plate calipers areindicated for each plate type and size. The left side of the diagramshows data for 8.75 inch plates whereby the J plate rigidity is aboutthree times higher than S at significantly reduced caliper and cost. Theright side of the diagram shows data for 10.25 inch plates whereby Jplated rigidity is more than seven times higher S at the same caliper.The open circle point corresponds to an estimated rigidity for the 10.25inch J plate that is scaled down in caliper so that plate material costsare equivalent to S.

The scaled J caliper X is calculated as X=(19 mil)(2.9 cents/3.8 cents).The theoretical rigidity R1 at equivalent cost for the downscaledcaliper is calculated as:

(R1/R2)=(14.5 mil/19 mil) exp N

where R2 is the experimental rigidity at 19 mil and N=1.816 is thecaliper exponent value for the Dixie Superstrong 10.25 inch plate designwhich is obtained from the general equation for rigidity:

R=(KE) TexpN

where E is Young's modulus, K is a shape constant, and T is caliper. Thedata set forth in FIG. 34 demonstrate that the rigidity of the J plateof this invention is significantly higher at equivalent or lowermaterial cost than commercial polystyrene polymer based plates.

In FIG. 35, the heat resistance performance for mica filledpolypropylene 10.25 inch plates (J), having an average caliper of 19 ml(J) is compared with (S) polystyrene based plates (S) of the same sizeand caliper. A measure of heat resistance is dynamic flexural storagemodulus E′, as measured with the Rheometrics Solids analyzer at 10rad/sec. Higher E′ values indicate increased stiffness and improveddimensional stability. Dynamic mechanical sprectroscopy is a commontechnique used for evaluation of viscoelastic properties of polymericmaterials with respect to temperature and input frequency (deformationtime scale). Dynamic mechanical properties of flat rectangular specimensof S plate material and PP/mica sheet of this invention were subjectedto flexural deformation at 10 rad/sec, using the Rheometrics SolidsAnalyzer RSAII instrument, manufactured by Rheometric Scientific, andequipped with a dual cantilever bending fixture. Temperature scans wereconducted at 0.05% strain using 2° C. temperature steps with a 0.5minute soak time at each temperature. From the time lag between inputstrain delivered by the driver motor and the stress output measured bythe transducer, values of material complex modulus E* are obtained. Theparameter E* is formally expressed as E*=E′+iE″, where E′ is the storagemodulus (purely elastic term) and E″ is the loss modulus (purely viscousterm). The storage modulus E′ is defined as the stress in phase with thestrain divided by the strain, which gives a measure of the energy storedand recovered per cycle. The loss modulus E″ is defined as the stress 90degrees out of phase with the strain divided by the strain, which givesa measure of the energy dissipated per cycle. The ratio of loss modulusto storage modulus is commonly known as the damping (tan delta) wheredelta is the phase angle between stress and strain. The dynamic storageflexural modulus E′ is the operative measure of heat resistanceperformance, where higher values mean higher performance. At ambientconditions (77° F.), E′ for mica filled polypropylene plates of thisinvention is appreciably higher than for S. At 250° F., whichcorresponds to aggressive temperatures which are commonly encountered inthe microwave heating or cooking of greasy foods, the heat resistance ofJ plates of this invention is significantly superior to the platesmanufactured by S, as further demonstrated below in connection withmicrowave cooking trials.

TABLE 20 MICROWAVE COOKING TEST RESULTS FOR PLATES J AND S PLATE TYPEFOOD TYPE J S Donut Pass Sugar glazing sticks Broccoli/cheese PassSignificantly deforms Pepperoni pizza Pass Moderate deformation,Staining Barbecue pork Slight stain Significant stain/warpagePancake/syrup Pass Significant warpage Beans & pork Pass Significantwarpage Butter Slight warpage Significant warpage Bacon Moderate warpageSignificant Localized melting, no leak warpage Rubbery plate flows andSticks to glass tray

Microwaveability

Fort James Corporation (J) plate specimens of this invention and platesmanufactured by Solo Cup Company (S) were tested in themicrowave-(Sainsung model MW 8690) with a variety of foods. The highestpower setting (10) was used in all cases and cooking/heating times andprocedures corresponded to food manufacturer instructions on thepackages. Most tested foods were of the frozen microwaveable type andwere placed in a semi-thawed state directly on plates prior to cooking.When appropriate, a loose covering of wax paper was employed during thecooking process. After cooking, the plates were gently washed with warmwater and inspected. The following are the detailed test results whichare also summarized in above Table 20.

TEST #1 RESULTS—Sugar Glazed Donut

J A large, oval shaped sugar glazed plain donut was microwaved on theplate of this invention for 60 seconds. The sugar glazing melted,bubbled, and flowed on the plate. The boiling sugar and grease mixturecaused the bottom of the plate to feel very warm but the plate exhibitedno warping, no staining, no softening, and no soak-through. The platewas cool enough to be safely handled. The residue of the donut waseasily washed off and the appearance of the used is plate was excellent.

S The bottom of the plate got hot and slightly deformed with nosoak-through, however, sugar stuck to the plate.

TEST #2 RESULTS—Broccoli With Cheese Sauce

J Green Giant 10 oz. Broccoli with cheese sauce was removed from theflexible pouch and heated for five minutes in the microwave on the platewith loose covering of wax paper. The cheese melted and bubbled on theplate without sticking. The plate bottom was warm, but no soak-throughand no loss of dimensional stability was observed. After washing, nostaining was observed and the appearance of the used plate wasexcellent.

S The plate bottom got hot and significantly deformed with nosoak-through.

TEST #3 RESULTS—Pepperoni pizza

J Tombstone 7 oz. Pepperoni pizza was cooked on an uncovered plate for 4minutes. The cheese melted and started bubbling about halfway throughthe test. The molten cheese mingled with the hot liquid fat extrudedfrom the pepperoni and dripped on the sides of the crust onto the plate.No sticking, no soak-through, no staining, and no loss in platedimensional stability was observed and the appearance of the used platewas excellent.

S The plate bottom got hot and moderately deformed with no soak-through.The greasy reddish stain from oil in pepperoni could not be completelywashed off.

TEST #4 RESULTS—Microwave Kid Meal

Pork Rib Patties, Barbecue Sauce, Fries, Honey Corn Bread

J A quick meal preparation simulation test was conducted using a Swanson7.2 oz. microwave kids'meal with ingredients consisting of partiallycooked boneless pork rib patties, barbecue sauce, fries, and honey cornbread. The food was transferred from the compartmented tray onto theplate. Sauce was spooned on top of the pork meat and was allowed to dripon the sides of the patties and onto the plate. The cornbread batter wasspooned out and was placed on the plate next to the fries. The food wasloosely covered with wax paper and cooked for 3.5 minutes. Examinationafter microwaving showed that the cornbread was fully cooked and therewas no sticking or damage to the plate. The fries and pork meat withsauce caused no soak-through and no loss in plate dimensional stability.Washing of plate revealed the presence of slight staining from barbecuesauce. Overall, the appearance of the used plate was very good.

S The plate bottom deformed mainly from pork meat with considerablestaining from the barbecue sauce without soak-through.

TEST #5 RESULTS—Beans With Pork and Tomato Sauce

J Beans with pork and tomato sauce (8 oz. Can) were placed on the plate,covered with wax paper and heated for 2 minutes near boiling. The bottomof plate got hot, but the rim was cool to touch. The hot plate bottomexhibited no bulging and also, when the hot food plate was handled bythe rim there was no perceived loss in dimensional stability. Nosoak-through, no warping and no staining was observed. The appearance ofthe plate was excellent.

S The plate bottom became very hot and severely deformed with nosoak-through and when handled by the rim, the plate felt like it had lowrigidity.

TEST #6 RESULTS—Pancakes With Syrup and Precooked Bacon

J In this test, Swanson microwave pancakes and bacon breakfast (4.5 oz.size) were used. The semi-thawed meal consisted of three pancakes andthree partially, precooked bacon strips. The pancakes and bacon wereremoved from the tray in carton and placed on plate. Approximately 5teaspoons of pancake syrup was spooned over the pancakes and theassembled meal was covered with wax paper and microwaved for 2 minutes.Although the bottom of the plate got hot, the overall plate performancewas excellent, i.e. no warpage, no soak-through, no loss in dimensionalstability, and no staining. Some hot grease was exuded by the baconduring crisping but there was no observed damage to the plate. Theappearance of the used plate was excellent.

S The plate bottom became hot and significantly deformed (especially inareas where bacon was placed), but no soak-through was observed and whenhandled by the rim, the plate felt soft.

TEST #7—Butter

J Butter (5-tsp. chunk) was placed on the plate and was loosely coveredwith wax paper and was microwaved for 3 minutes. The butter meltedcompletely and covered the whole plate bottom. The butter began boilingtoward the end of the test. The plate bottom got very hot and becameslightly warped but no soak-through. The rim of the plate felt cool totouch enabling safe removal of the plate from the microwave oven. Asmall portion of the butter became charred but was easily washed off theplate. Overall plate performance was good.

S The plate bottom became very hot and was significantly warped but nosoak-through was observed and the greasy film residue could not bewashed off completely. Plate felt soft and rubbery when handled by therim.

TEST #8 RESULTS—Bacon

J Three strips of raw, cured bacon were wrapped in three sheets of papertowel and cooked for 5 minutes. All of the bacon became crispy and about20% of it was charred. The bottom of plate got very hot but most of therim area was relatively cool to the touch. Grease exuded from bacon andsoaked through the towel. The grease pooled on the plate bottom, sideand on some rim areas. The grease which pooled in some rim regionscaused localized melting of the plate but no holes were formed. The hotgrease which pooled on plate bottom caused significant warpage but nosoak-through. Overall plate performance for Test #8 was lesssatisfactory than Test #7.

S When the raw bacon was wrapped in paper toweling and cooked on the Splate, the bottom became very soft and stuck to the glass tray in themicrowave. Under such hot grease conditions, the adhering polymerregions underwent localized melting and stretched when the plate waslifted off the glass tray. The plate was severely warped but no holesformed and no soak-through was noticed.

With the possible exception of raw bacon, the behavior of the J plate ofthis invention in the microwave oven is considered excellent with avariety of aqueous, greasy/fatty, sugary food combinations. No unusualor off odors were detected during and after cooking for each type offood directly on the plate. The foregoing data demonstrates the superiorproperties of the plates of this invention.

Crack Resistance

Low temperature crack resistance of rigid plates is of paramountimportance when considering that product must survive during storage andshipping to point of sale. Normally, it is difficult to improve crackresistance or reduce brittleness of rigid polymeric materials withoutreducing the stiffness which is usually the case when introducingexcessive amounts of softer extensible materials such as polyethylenes,rubber modified resins and the like. In order to be successful inimparting crack resistance without significantly reducing stiffness, onemust add relatively low amounts of polyethylene or rubber modifiedadditives, generally in the range of several to about 5 wt%. However,this invention shows that addition of low levels of polyethylene aloneis not sufficient to promote crack resistance whereby the desired resultis produced by a synergistic binary combination of polyethylene andTiO2. Such low odor products have high crack resistance which rendersthem useful in the commercial sense.

EXAMPLES 63-70

There is provided in a still further aspect of the invention toughened,crack resistant articles. It has been found thatpolypropylene/mica/polyethylene/titanium dioxide formulations without acoupling agent resist cracking. Generally, the articles have thecomponents set forth in Table 21, in the amounts mentioned above in thesummary of the invention herein. In Table 21, it is demonstrated thatpolyethylene/titanium dioxide exhibit synergy in resisting cracking.

TABLE 21 Low Temperature crack data for 9 inch plates made of PP/30%mica/10% CaCO₃ modified with various combinations of TiO₂, polyethylene,or coupling agent Coupling Example TiO₂ LLDPE HDPE Agent Percent Cracked# (wt %) (wt %) (wt %) (wt %) plates at 0 F.** 63 — 4 — — 100 (n = 5) 64— — — 2.5 100 (n = 5) 65 1.9 — — — 100 (n = 5) 66 — 4 — 2.5 100 (n = 5)67 1.9 0 0 2.5 100 (n = 5) 68 0.5 4 — 2.5  60 (n = 5) 69 0.5 4 0 0  0 (n= 5) 70 0.5 0 4 0  0 (n = 10) *Coupling agent is maleic anhydridemodified PP grade Aristech Unite NP-620: other ingredients are: Mica =Franklin Minerals L 140, CaCO3 = Huber Q325, other ingredients are: Mica= Franklin Minerals L 140, CaCO3 = Huber Q325, PP = Exxon EscorenePP4772, LLDPE = Novapol Novachemical G1-2024A **percentage of plateswhich cracked at 0° F. for specimen sets comprised of the indicatesnumber n

Crack resistance of Examples 63 through 70 was evaluated in thelaboratory according to method set forth below which was found useful asan investigative tool for optimizing the formulation with variouscombination of TiO2, polyethylene, or coupling agent. A laboratoryprocedure was devised and used to evaluate the crack resistance ofplates. Specifically, following is a description of test instruments andassociated fixtures used to subject plates to a repeatable rim crushingforce. The model numbers of standard equipment used on this procedureare recited below and additional fixtures used in these tests wereemployed as follows:

Instron - Model #55R402 was used which was equipped with InstronEnvironmental Chamber Model #3111. The Instron environmentalchamber-Model #3111 was modified to control low temperatures with liquidnitrogen. It was equipped with a control solenoid mounted on the rear ofthe cabinet and an electronic control module mounted on the controlpanel assembly. The temperature within the chamber was controlled inrelationship to the setpoint on the front panel temperature dial. Athermocouple within the chamber provides feed back to the device. Amercury thermometer was placed in the chamber and oriented so thattemperature within the chamber was visible through an insulated glassdoor. It was monitored and adjusted to 0° C. using the panel temperaturedial.

A push rod was attached to the load cell of the instron and was passedthrough an opening in the top of the environmental chamber. A circularmetal device measuring 100 mm in diameter and 10 mm in thick wasattached to the end of the push rod inside the chamber. This circularmetal device was used to contact the edge of a plastic plate duringtesting.

The plate support fixture was placed on a circular metal base supportwhich measured 140mm in diameter by 14 mm thick. This metal base supportwas located just above the inside floor of the environmental chamber. Itwas attached to a support rod that passes through the floor of theenvironmental chamber and attached to the base of the instron. Centeringstops were provided on the metal base support so that the plate supportfixture could be repeatedly placed at the same location in theenvironmental cabinet.

The plate support fixture is constructed of 5-mm thick sheets ofplexiglas.

The main base of this fixture measures 100×125 mm. The 125-mm dimensionrepresents the width of the front of the mixture. The edge of the 125 mmside of a second plexiglas panel measuring 160×125 mm was permanentlyattached to the plexiglas main base. This panel was attached at a 90°angle to the main base and 35 mm in from the front edge. An L shapedplexiglas component was attached to the main base behind and parallel tothe permanent panel by thumbscrews. Two 20-mm long slots were providedin the base of the L shaped component to allow attachment and providemovement for adjustment to hold the test plate. The short leg or base ofthe L shaped component faces the rear of the fixture. A block measuring40×25×15 mm thick was permanently attached at the upper most end at thecenter of the L shaped component. This block is located on the frontside of the moveable component or just opposite the short leg of the Lshaped component, while an adjustable plate stop was attached to oneside of the moveable L shaped component.

The methodology for testing the crack resistance of plates was asfollows. The test plate was secured in a vertical position on edge inthe plate support fixture. The bottom of the test plate was placedagainst the permanently attached plexiglas panel of the plate supportfixture. The thumbscrews were loosened on the moveable portion of theplate support fixture. The L shaped moveable component was moved towardthe plate. The plate was held in a vertical position by the fixedplexiglas panel and the block which was attached to the wall of the Lshaped moveable component.

The plate stop located on the L shaped moveable component was adjustedso that the center of the plate would align with the center of the platesupport fixture. The plate support fixture along with the test platesecured in a vertical position was placed on the metal base support inthe environmental chamber. The instron was adjusted so that the push rodcrush assembly was located 0.5 inches above the plate edge.

Prior to the test, the environmental chamber was adjusted to 0° F. Afterplacement of the plate support fixture along with the test plate securedin a vertical position in the environmental chamber, the chamber had tore-establish 0° F. This time period was about 30 seconds. Afterre-establishment of the test temperature, the plate was conditioned foran additional five minutes prior to the test.

The crosshead speed of the instron was set at 40 inches per minute.After the five minute conditioning time period, the instron wasactivated and the edge crushing force applied. A set of five or a set often replicate plates was tested for each condition. The total number ofplates tested and the total number plates showing rim crack failure foreach condition tested are reported in Table 21. In addition, thepercentage of plates which cracked was calculated as shown above.

The above formulations for crack resistance testing were compounded inthe temperature range of 400 to about 425 F on commercial Banburyequipment using batch sizes in the range of 150-200 lb and nominalmixing times of 3 min followed by underwater pelletizing.

Pellets were subsequently extruded at 370 F as cast sheets in the rangeof 18 mil. Sheet line conditions also included a screw RPM value of 100,a chill roll temperature of 130 F. Plates were subsequently vacuumthermoformed using a female mold, trimmed, and thereafter tested forcrack resistance.

Data on Examples 63 through 65 show that presence of TiO2, polyethylene,or coupling agent alone is not sufficient to promote crack resistance ofplates comprised of PP/mica/CaCO3. In addition, data on Examples 66 and67 show that binary combinations of polyethylene with coupling agent orTiO2 with coupling agent are two cases which are also not sufficient forimparting crack resistance. Furthermore, the tertiary combination ofTiO2, polyethylene, and coupling agent (Example 68) also does not impartsufficient crack resistance, as evidenced by the majority of sampleswhich exhibit cracking. Rather, the useful additive packages of thisinvention (Examples 69 and 70) comprises the binary system ofpolyethylene (either LLDPE or HDPE) with at least 0.5 wt. % TiO2 wherebycrack resistance is excellent as evidenced by no cracked samples.

EXAMPLES 71-78

Additional plates were fabricated in accordance with the foregoingprocedures and compositions; crack testing results appear in Table 22below

TABLE 22 Crack Data and Physical Properties for Various CompoundedFormulations Base Formulation: PP/30% Mica/10% CaCO₃ Formulation MeltFlow Filler 9″ Plate Product TiO₂ PE Coupling g/10 min. @ ContentFlexural Modulus Rigidity Weight Crack Data @ 0° F. Example (wt. %) (4wt. %) Agent* 230° C. (Wt. %) Tangent (psi) (grams/0.5°) (grams) (#Cracked Total) 71 0 LLDPE No 1.45 39.4 505,000 288 19.3 5/5 72 1.9 LLDPENo 1.64 40.6 581,600 422 23.13 0/5 73 1.2 LLDPE No 2.05 39.8 578,500 38522.12 0/5 74 0.5 LLDPE No 1.77 38.6 487,500 286 20.65 0/5 75 l.9 HDPE No1.5 40.6 637,500 436 22.70 1/5 76 1.9 0 Yes 1.9 39.0 717,585 417 21.255/5 77 1.9 LLDPE Yes 1.6 39.6 494,000 391 21.6 5/5 78 1.9 0 Yes 1.2 40.3593,000 353 20.8 5/5 *When present, coupling agent concentration is 2.5%

What is claimed is:
 1. A crack-resistant, thermoformed food containerhaving a wall thickness from about 10 to about 80 mils consistingessentially of from about 40 to about 90 percent by weight of apolypropylene polymer, from about 10 to about 50 percent by weight mica,from about 1 to about 15 percent by weight polyethylene and from about0.1 to about 5 weight percent titanium dioxide.
 2. The crack-resistant,thermoformed food container according to claim 1, wherein said basicorganic or inorganic compound comprises calcium carbonate and saidcalcium carbonate is present in an amount of from about 5 to about 20weight percent.
 3. The crack-resistant, thermoformed food containeraccording to claim 1 wherein polyethylene is present from about 2.5 toabout 15 percent by weight.
 4. The crack-resistant, thermoformed foodcontainer according to claim 3, wherein polyethylene is present fromabout 4 to about 5 weight percent.
 5. The crack-resistant, thermoformedfood container according to claim 1, wherein titanium dioxide is presentfrom about 0.1 to about 3 weight percent.
 6. The crack-resistant,thermoformed food container according to claim 5, wherein titaniumdioxide is present from about 0.25 to about 2 percent by weight.
 7. Thecrack-resistant, thermoformed food container according to claim 1wherein titanium dioxide is present in an amount of at least about 0.5percent by weight.
 8. The crack-resistant, thermoformed food containeraccording to claim 1, wherein said article has a wall caliper of fromabout 10 to about 50 mils.
 9. The crack-resistant, thermoformed foodcontainer according to claim 8, wherein aid article has a wall caliperof from about 15 to about 25 mils.
 10. The crack-resistant, thermoformedfood container according to claim 1, wherein said mica is an untreatedmica.
 11. The crack-resistant, thermoformed food container according toclaim 1, wherein said polypropylene polymer is isotactic polypropylene.12. The crack-resistant, thermoformed food container according to claim11, wherein said isotactic polypropylene has a melt index of from about0.3 to about
 4. 13. The crack-resistant, thermoformed food containeraccording to claim 12, wherein said isotactic polypropylene has a meltflow index of about 1.5.
 14. The crack-resistant, thermoformed foodcontainer according to claim 1, wherein said polyethylene is highdensity polyethylene.
 15. The crack-resistant, thermoformed foodcontainer according to claim 1, wherein said polyethylene is linear lowdensity polyethylene.